As of Angular Package Format v10, we no longer ship a `fesm5` and
`fesm5` output in packages. We made this change to the `ng_package`
rule but intentionally did not clean up related build actions.
This follow-up commit cleans this up by:
* No longer building fesm5 bundles, or providing esm2015 output.
* No longer requesting and building a third flavor for ESM5. We can
use TSC to downlevel ES2015 sources/prodmode output similarly to how it
is done in `ng-packagr`.
The third output flavor (ESM5) resulted in a build slow-down as we
required a full recompilation of sources. Now, we only have a single
compilation for prodmode output, and then downlevel it on-demand
to ES5 for the UMD bundles. Here is timing for building the release
packages in `angular/angular` before this change, and afterwards:
* Before: 462.157s = ~7.7min
* After: 339.703s = ~5.6min
This signifies a time reduction by 27% when running
`./scripts/build/build-packages-dist.sh`.
PR Close#37623
62a85f5e55