Expose rich repository pickers as API

[joyceerhl]

The following extensions contain rich pickers for working with git repositories:

• GitHub Repositories
• git-base (built-in)

The git-base extension exposes API allowing other extensions to contribute entries to its repository pickers. The GitHub Repositories extension does not yet expose such API.

vscode/extensions/git-base/src/api/git-base.d.ts

Lines 9 to 12 in bfad20b

	export interface API {
	registerRemoteSourceProvider(provider: RemoteSourceProvider): Disposable;
	pickRemoteSource(options: PickRemoteSourceOptions): Promise<string | PickRemoteSourceResult | undefined>;
	}

This issue tracks evaluating existing pickers across both extensions and making the rich pickers in GitHub Repositories available to other extensions, potentially by enhancing the pickers in git-base or by exposing extension API on the GitHub Repositories extension modeled after git-base API.