Currently if an Angular library has multiple unnamed module re-exports, NGC will
generate incorrect metdata if the project is using the flat-module bundle option.
e.g.
_public-api.ts_
```ts
export * from '@mypkg/secondary1';
export * from '@mypkg/secondary2';
```
There are clearly two unnamed re-exports in the `public-api.ts` file. NGC right now
accidentally overwrites all previous re-exports with the last one. Resulting in the
generated metadata only containing a reference to `@mypkg/secondary2`.
This is problematic as it is common for primary library entry-points to have
multiple re-exports (e.g. Material re-exporting all public symbols; or flex-layout
exporting all public symbols from their secondary entry-points).
Currently Angular Material works around this issue by manually creating
a metadata file that declares the re-exports from all unnamed re-exports.
(see: https://github.com/angular/material2/blob/master/tools/package-tools/build-release.ts#L78-L85)
This workaround works fine currently, but is no longer easily integrated when
building the package output with Bazel. In order to be able to build such
libraries with Bazel (Material/flex-layout), we need to make sure that NGC
generates the proper flat-module metadata bundle.
PR Close#29360
105cfaf5e4