[rush] Expose Rush Command Line Parser via API

[william2958]

Summary

This MR introduces the RushCommandLineAPI class, which exposes the set of actions available from the rush command line and their corresponding parameter details through a getSpec static function. This allows us to expose rush's set of command line actions without directly exposing the RushCommandLineParser.

This is useful for other rush tools that may need to work with the available rush actions such as by displaying them through a GUI (such as in the rush vscode extension)

Details

How it was tested

Tested by comparing the output to the output generated by the RushCommandLineParser class.

Impacted documentation