fix(@angular/build): merge component stylesheet metafiles in a stable order - #34210

Thanks for investigating this! However, there are a couple of concerns with this approach:

1. Stats accuracy: outputs[file].inputs in an esbuild metafile is intended to list all input source files that contributed to that output file. By sorting and continuing to shallowly overwrite with Object.assign(result.metafile.outputs, metafile.outputs), we deterministically drop inputs (as seen in the test where src/app/a/shared.css is completely missing from outputs['shared.css'].inputs). When an output already exists in result.metafile.outputs, we should merge existingOutput.inputs rather than replacing the entire output entry.
2. Performance: [...additionalResults].sort(...) creates and sorts an array of [key, value] tuples across all component stylesheets on every build and rebuild in the critical path, even when statsJson is disabled. In large apps with thousands of components, this introduces unnecessary allocations and overhead. If deterministic key ordering for stats.json is required, that can be done when generating/serializing the stats JSON (where options.stats is enabled) rather than in the compilation plugin's onEnd callback.

Both points taken, and this replaces what I said to the bot above. Pushed as two fixups.

• The merge now unions inputs when an output already exists, and builds a new object for the merged entry. The new object matters: the stylesheet bundler caches its result across rebuilds and the clone shares each output's inputs, so assigning in place carried one stylesheet's input into the other's entry on later rebuilds. The sort is gone.
• The stats files are serialised with sorted keys, behind options.stats. onEnd is otherwise as it was.
• Three specs: both inputs listed on every build; both stats files sorted; and a five-build watch test that changes one of two identical stylesheets, restores it, and changes it again, the ordering that exposes an in-place merge.

Each spec fails against the code it guards, and the application target passes in full. One detail for the record: unminified CSS carries a source-path comment, so identical stylesheets share a hashed name only when styles are minified, which is why this stayed hidden in development builds.