[plugin] Implement SCM Repository selected event

[vinokurig]

What it does

Implement SCM Repository selected event: https://github.com/microsoft/vscode/blob/a50cf110d96fbe50fc460a6de14ade5b6b060dd4/src/vs/vscode.proposed.d.ts#L673-L684
Removed duplicated SourceControlResourceDecorations interface.

How to test

1. Open a workspace with more than one Git repositories.
2. Clone to the workspace folder and compile the test plugin: https://github.com/vinokurig/Test.git
3. Start hosted instance with the plugin.
4. Select the / SCM repository (this is a view of a dummy SCM repository):
   

See the notification that is fired inside the event handler.
Select other repository again.
See the notification that the repository is NOT selected.

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[akosyakov]

@vinokurig I could not figure out how I can test that a source control is properly unselected with the proposed extension. We need an extensions which has several source controls and show notifications when one get unselected or selected. @theia/git extension should be removed during testing.

[vinokurig]

@akosyakov I think I've understood your point, I've reworked the logic and now you can test this against the plugin provided above that I've changed as well. To apply the plugin you need to disable built in Git extension and paste any folder paths as a repository url: https://github.com/vinokurig/Test/blob/2f48915bab1487d5998ceed06c68d60c898f5ffc/src/scm-plugin-backend.ts#L9-L11

[akosyakov]

@vinokurig it looks better now! but i don't see initial notification and after i switch to another repo there is no notification that an initial repository is unselected.

[vinokurig]

@akosyakov

@vinokurig it looks better now! but i don't see initial notification and after i switch to another repo there is no notification that an initial repository is unselected.

I've fixed that by extracting the logic to a method as you recommended.

[akosyakov]

it works very nice now!

[akosyakov]

@vinokurig please rebase and if ci is green please merge, don't forget to address the outstanding comments