This PR added tests for Next.js TypeScript plugins, specific for client-boundary. Updated the readme and removed the legacy fixture.

_Relanding #79151, now ignoring TS AST nodes when checking whether all
exported module items are async functions._

This fixes an error where we incorrectly showed the following compiler
error when using Turbopack:

```sh
Ecmascript file had an error
> 1 | 'use cache'
    | ^^^^^^^^^^^
  2 |
  3 | import { useStuff } from './client-module'
  4 |

The "use cache" directive must be at the top of the file.
```

The directive was regarded as not being at the top of the file, because
the React transform (`EcmascriptInputTransform::React`) injects a
variable declaration for React Refresh (e.g. `var _s =
__turbopack_context__.k.signature`) at the top of the file, before the
`"use cache"` directive.

We can fix this by ensuring that the server action transform (should
really be called "server _function_ transform") runs first.

As a consequence, the transform now needs to be able to parse JSX AST
nodes, which was already explicitly implemented.

closes NAR-130

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## What?

Allows e.g. ```import(`${url}`)``` when in node_modules. This makes
monaco-editor work automatically when it's correctly imported in e.g. a
`useEffect`.

- [x] Apply change 
- [x] Verify against local reproduction
- [x] Add test case

Fixes #72613
Fixes PACK-4602