vscode: Support property SourceControlInputBox#visible

[KevinK-9]

What it does

Implements Support specifying whether an SourceControlInputBox is visible.

Issues Adressed

• Closes [vscode] Support property SourceControlInputBox#visible #11140

How to test

• ToDo

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

[vince-fugnitto]

@KevinK-9 thank you for the contribution, do you need help with testing?

[xai]

For testing, I tried to create a simple vscode extension.

To test, install the test extension vscode-extension-sourcecontrol-inputbox-11140-0.0.1.vsix in your theia workspace from your filesystem.
It provides a command SourceControlInputBox: Status to display the properties of sourceControl.inputBox.
(It also provides SourceControlInputBox: Hide and SourceControlInputBox: Show to change the respective Boolean.)

Using the patch from this PR (I rebased it on current master though), theia behaves the same as VSCode, at least in my setup.

[xai]

@vince-fugnitto I suggest we close this in favor of #11412, which includes the working patch (thanks @KevinK-9!) and a respective sample extension for testing. If there are any additional requirements to get Kevin's patch in, I will gladly take care of it.