…tter#156502)

Allows applying of `include_flutter.groovy` via the `apply from:` syntax, which allows using a host app that is using the Gradle Kotlin DSL (the default these days when creating an Android app in AS).

Explanation: The `include_flutter.groovy` script is currently not able to be called by Kotlin gradle files, because it is [intended to be invoked with the following lines](https://docs.flutter.dev/add-to-app/android/project-setup#depend-on-the-modules-source-code):
```
setBinding(new Binding([gradle: this]))                                // new
evaluate(new File(                                                     // new
    settingsDir.parentFile,                                            // new
    'flutter_module/.android/include_flutter.groovy'                   // new
))
```

`setBinding` isn't part of the Kotlin gradle DSL, and there isn't (that I can find) an easy Kotlin equivalent. If this binding isn't set, the reference to `gradle` in `include_flutter.groovy` is wrong, which breaks the script.

This PR modifies `include_flutter.groovy` to also support being invoked through the standard way of invoking a script via the Gradle Groovy/Kotlin DSLs, which is `apply from:` (or it's slightly different Kotlin syntax). The start of the script identifies which of the two approaches is being used by checking if the binding is set, and then initializes some variables differently depending on the case.

If we land this, I believe we should update the example Gradle files for both the `kts` and `groovy` cases to prefer the `apply from` syntax as I think this is the syntax most developers would be more familiar with already seeing in their Gradle files.

…app (flutter/flutter#156502)

…tter#156502)

Allows applying of `include_flutter.groovy` via the `apply from:` syntax, which allows using a host app that is using the Gradle Kotlin DSL (the default these days when creating an Android app in AS).

Explanation: The `include_flutter.groovy` script is currently not able to be called by Kotlin gradle files, because it is [intended to be invoked with the following lines](https://docs.flutter.dev/add-to-app/android/project-setup#depend-on-the-modules-source-code):
```
setBinding(new Binding([gradle: this]))                                // new
evaluate(new File(                                                     // new
    settingsDir.parentFile,                                            // new
    'flutter_module/.android/include_flutter.groovy'                   // new
))
```

`setBinding` isn't part of the Kotlin gradle DSL, and there isn't (that I can find) an easy Kotlin equivalent. If this binding isn't set, the reference to `gradle` in `include_flutter.groovy` is wrong, which breaks the script.

This PR modifies `include_flutter.groovy` to also support being invoked through the standard way of invoking a script via the Gradle Groovy/Kotlin DSLs, which is `apply from:` (or it's slightly different Kotlin syntax). The start of the script identifies which of the two approaches is being used by checking if the binding is set, and then initializes some variables differently depending on the case.

If we land this, I believe we should update the example Gradle files for both the `kts` and `groovy` cases to prefer the `apply from` syntax as I think this is the syntax most developers would be more familiar with already seeing in their Gradle files.

…tter#156502)

Allows applying of `include_flutter.groovy` via the `apply from:` syntax, which allows using a host app that is using the Gradle Kotlin DSL (the default these days when creating an Android app in AS).

Explanation: The `include_flutter.groovy` script is currently not able to be called by Kotlin gradle files, because it is [intended to be invoked with the following lines](https://docs.flutter.dev/add-to-app/android/project-setup#depend-on-the-modules-source-code):
```
setBinding(new Binding([gradle: this]))                                // new
evaluate(new File(                                                     // new
    settingsDir.parentFile,                                            // new
    'flutter_module/.android/include_flutter.groovy'                   // new
))
```

`setBinding` isn't part of the Kotlin gradle DSL, and there isn't (that I can find) an easy Kotlin equivalent. If this binding isn't set, the reference to `gradle` in `include_flutter.groovy` is wrong, which breaks the script.

This PR modifies `include_flutter.groovy` to also support being invoked through the standard way of invoking a script via the Gradle Groovy/Kotlin DSLs, which is `apply from:` (or it's slightly different Kotlin syntax). The start of the script identifies which of the two approaches is being used by checking if the binding is set, and then initializes some variables differently depending on the case.

If we land this, I believe we should update the example Gradle files for both the `kts` and `groovy` cases to prefer the `apply from` syntax as I think this is the syntax most developers would be more familiar with already seeing in their Gradle files.

_Description of what this PR is changing or adding, and why:_

Improves and adds documentation for launching Flutter from Kotlin and
Compose-flavored Android apps

_Issues fixed by this PR (if any):_

_PRs or commits this PR depends on (if any):_

Depends on flutter/flutter#156502. Must either use the `master` channel
or `stable` after that code reaches it.

Changes can be previewed on the staging built at these URLs:
*
[`/add-to-app/android/project-setup`](https://flutter-docs-prod--pr11345-launch-flutter-from-compose-wlgslbu8.web.app/add-to-app/android/project-setup)
*
[`/add-to-app/android/add-flutter-screen`](https://flutter-docs-prod--pr11345-launch-flutter-from-compose-wlgslbu8.web.app/add-to-app/android/add-flutter-screen)

## Presubmit checklist

- [x] This PR is marked as draft with an explanation if not meant to
land until a future stable release.
- [x] This PR doesn’t contain automatically generated corrections
(Grammarly or similar).
- [x] This PR follows the [Google Developer Documentation Style
Guidelines](https://developers.google.com/style) — for example, it
doesn’t use _i.e._ or _e.g._, and it avoids _I_ and _we_ (first person).
- [x] This PR uses [semantic line
breaks](https://github.com/dart-lang/site-shared/blob/main/doc/writing-for-dart-and-flutter-websites.md#semantic-line-breaks)
of 80 characters or fewer.

---------

Co-authored-by: Khanh Nguyen <[email protected]>

…app (flutter/flutter#156502)

…app (flutter/flutter#156502)

…app (flutter/flutter#156502)

…app (flutter/flutter#156502)

…app (flutter/flutter#156502)