perf(@angular/build): consolidate component stylesheet bundling with shared load result cache

[alan-agius4]

Replaces per-stylesheet esbuild.context proliferation in ComponentStylesheetBundler with ephemeral single-shot esbuild.build() invocations and a shared, persistent MemoryLoadResultCache.

Key Improvements

1. Eliminates Go process IPC context proliferation (500 active goroutines/contexts -> 0 lingering contexts).
2. Cross-component Sass partial & preprocessor cache sharing via unified MemoryLoadResultCache.
3. In-flight compilation deduplication coalescing concurrent requests.
4. Optimized set intersection invalidation (O(min(|A|, |B|))) accelerating large-scale file invalidations by up to 70x.

Comprehensive Benchmarks

1. Cold Compilation Throughput & Latency (Mean Duration)

Workload	Baseline	Consolidated	Speedup	Latency Reduction
100 Components (Cold)	114.96 ms	98.74 ms	1.16x	-14.1%
300 Components (Cold)	358.37 ms	315.68 ms	1.14x	-11.9%
500 Components (Cold)	609.68 ms	530.87 ms	1.15x	-12.9%

2. Memory Footprint (500 Components)

Metric	Baseline (Contexts)	Consolidated (Shared Cache)	Delta / Improvement
Persistent Go IPC Contexts	500 active	0 contexts	-100.0% (Eliminated)
V8 Heap Used Delta	+10.22 MB	+5.79 MB	-43.3% Heap Reduction
Resident Set Size (RSS) Delta	+27.60 MB	+16.30 MB	-41.0% RSS Reduction

3. Watch Mode Rebuild & Invalidation Latencies

Scenario	Baseline	Consolidated	Speedup Factor
Leaf Component Stylesheet Edit	7.96 ms	6.75 ms	1.18x Faster
Shared Sass Partial Edit	227.18 ms	206.63 ms	1.10x Faster
Branch Switch (500 modified / 500 components)	2.27 ms/op	0.14 ms/op	16.07x Faster
Large Switch (1,000 modified / 1,000 components)	28.38 ms/op	0.40 ms/op	70.65x Faster
No-Op / Touched File Rebuild	0.47 ms	0.29 ms	1.62x Faster

[alan-agius4]

/gemini review

[gemini-code-assist]

Code Review

This pull request refactors ComponentStylesheetBundler to run esbuild compilations directly instead of using BundlerContext, introducing custom caching and promise-based deduplication for both file and inline stylesheets. The review feedback highlights a potential bug where externalId remains a boolean if the cached identifier is missing, a performance optimization in the cache invalidation logic using set intersection, and a missing guard in extractResult that could lead to a TypeError if result.metafile is undefined.

[gemini-code-assist]

Code Review

This pull request refactors ComponentStylesheetBundler to perform direct esbuild compilation using build() instead of wrapping it in BundlerContext. It introduces in-memory caching for file and inline results, along with tracking active build promises to support incremental watch mode. The review feedback highlights critical race conditions and stale cache write issues in both file-based and inline stylesheet bundling when files are modified while a build promise is in-flight. It is recommended to clear pending promises on invalidation, ensure only active promises write to the cache, and extract a helper function to resolve absolute paths to reduce code duplication in #collectWatchFiles.