Use id of last module in chunk as name base for auto-generated chunks (…

…#3025)

* Use new FileEmitter for basic cases around assets. TODO: Replace asset
hooks completely, create tests for assets using the new hooks.

* Migrate assets to new file emitter

* Remove assetsById from Graph

* Implement emitFile for assets

* Internally use EmittedFile in the file emitter

* Deprecate emitAsset and ROLLUP_ASSET_URL

* Deprecate getAssetFileName

* Merge chunk emission into unified API and deprecated previous API

* Allow emitting files with fixed names

* Support unnamed assets

* Improve chunk name assignment

* Initial support for chunk file names

* Allow specifying explicit file names for emitted chunks

* Fix some TODOs

* Test ids remain stable when the transform hook is cached and make test
more stable

* Refine error handling

* Test some more errors

* Refine file emission

* Refactor file emitter to have a single code path for asset finalization

* Deduplicated emitted assets without a specific file name

* Only use the alias as name for a manual chunk if the chunk is not facade
for an entry point

* Generate separate facades for duplicate named user-defined entry points

* Always create facades for explicit file names

* Test edge cases

* Test and refactor handling of dynamic relative imports

* Use async-await in generate function, remove error condition

* Improve and test pattern validation

* Test file emitter edge cases

* Improve plugin error handling

* Add documentation

* Use id of last module in chunk as name base for auto-generated chunks