feat(@angular/build): enable chunk optimization by default with heuristics

[clydin]

Enable the advanced chunk optimization pass by default for applications with multiple lazy chunks to improve loading performance. A heuristic is introduced that automatically triggers this optimization when the build generates 3 or more lazy chunks. Developers can customize this behavior or disable it entirely using the NG_BUILD_OPTIMIZE_CHUNKS environment variable. Setting it to a number adjusts the threshold of lazy chunks required to trigger optimization, while setting it to false disables the feature if issues arise in specific projects.

[gemini-code-assist]

Code Review

This pull request introduces a heuristic-based chunk optimization pass that runs after the initial esbuild bundle. It replaces the previous unconditional optimization with a threshold-based approach (defaulting to 3 lazy chunks) and adds support for using Rollup or Rolldown as the optimization engine. Several improvements were made to the chunk optimizer to handle entry point identification and environment configuration. I have identified a potential issue regarding the removal of the entry point check, a concern about the compatibility of manifest generation with optimized chunks, and a suggestion to improve the robustness of the environment variable parsing.