perf(@angular/cli): cache root manifest and resolve restricted package exports in ng add

[clydin]

This change enhances the ng add command's performance by caching the root project manifest (package.json) to avoid redundant disk reads and JSON parsing during peer dependency conflict checks.

Additionally, it improves the robustness of package.json resolution for installed packages. Previously, resolving package.json could fail if a third-party package used the Node.js "exports" field without explicitly exporting its package.json. The CLI now correctly handles this by falling back to resolving the package's entry point and traversing upwards to find the manifest.

[gemini-code-assist]

Code Review

This pull request introduces two valuable improvements to the ng add command. First, it caches the root project's package.json, which effectively reduces redundant file reads and parsing, leading to better performance. Second, it enhances the package resolution logic to robustly locate a package's package.json even when it's not directly exported, by implementing a fallback strategy that traverses up from the package's main entry point.

My review has identified a couple of minor areas for improvement: an unused import and an empty catch block that could benefit from logging for better debuggability. Apart from these points, the changes are well-implemented and address the stated goals of performance and robustness.