…-lite's write bundles transform function (#33784)

## Current Behavior

When building Angular libraries with `ng-packagr` >20.3.0, the build
fails with:

```bash
TypeError: Cannot read properties of undefined (reading 'outputCache')
```
This occurs because `ng-packagr` v20.3.1 introduced a memory
optimization
([ng-packagr#3172](ng-packagr/ng-packagr#3172))
that calls `dispose()` on entry points after they're processed, setting
`entry.cache = undefined`.

Nx's custom `writeBundlesTransform` was iterating over **all** entries
in the graph, including already-disposed entry points, causing the crash
when accessing their cache.

## Expected Behavior

Angular library builds should succeed with `ng-packagr` >20.3.0,
including libraries with secondary entry points. Workspaces using lower
versions of `ng-packagr` should remain unaffected.

## Solution

Align with `ng-packagr`'s own pattern by using
`graph.find(isEntryPointInProgress())` to process only the currently
in-progress entry point, rather than iterating over all graph entries.

**Key changes:**

- Use `isEntryPointInProgress()` instead of iterating all entries with
`isEntryPoint()`
- Remove unused `BuildGraph` import (no longer creating a new graph)
- Update package node only when processing the primary entry point (more
efficient)
- Return nothing from the transform (original graph passes through, same
as ng-packagr)

This approach:

- Matches `ng-packagr`'s `writeBundlesTransform` implementation pattern
- Only accesses cache of the in-progress entry point (guaranteed not to
be disposed)
- Works with all supported `ng-packagr` versions (v19+) since
`isEntryPointInProgress()` has been available since v19

## Related Issue(s)

Fixes #33560