perf(@angular/cli): lazily initialize package manager in command context

[alan-agius4]

This change refactors the CommandContext to defer the initialization of the packageManager instance until it is first accessed. This optimization avoids unnecessary configuration discovery and disk I/O for commands that do not require the package manager, such as ng help, and certain shell completions.

As part of this refactoring:

• The packageManager property in CommandContext is now a Promise<PackageManager>.
• Internal command modules and utility functions have been updated to await the package manager's lazy initialization.
• In @angular-devkit/core, CoreSchemaRegistry was updated to rename _sourceMap to _sourceProvider and optimize the resolution of smart defaults by awaiting values during the _set operation.

[gemini-code-assist]

Code Review

This pull request refactors the CommandContext to treat the packageManager as a Promise, allowing for lazy initialization. This change requires updating multiple command modules to asynchronously resolve the package manager before use. Furthermore, the SmartDefaultProvider interface and the CoreSchemaRegistry have been updated to support asynchronous providers. Review feedback focuses on improving code readability and performance by avoiding redundant await calls on the packageManager promise in AddCommandModule and gatherVersionInfo.

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