plugin: Add support for activeColorTheme and onDidChangeActiveColorTheme API

[DucNgn]

CQ

• CQ approved: https://dev.eclipse.org/ipzilla/show_bug.cgi?id=22772

What it does

Closes #8635

• Supports:
  • activeColorTheme API: check what the current theme kind is (Light, Dark, or HighContrast)
  • onDidChangeActiveColorTheme API that fires an event when the color theme changed.

How to test

• Download test extension and include it in the plugins folder inside theia.
• Reload the application.

Test activeColorTheme:

• Call the command Echo Theme via the command palette.
• Observe a pop-up message with the exact kind of current color theme.

Test onDidChangeActiveColorTheme:

• Change theme kind by Preferences
• Observe a pop-up message upon the change of current theme.

Example of a pop-up message:

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

Signed-off-by: Duc Nguyen duc.a.nguyen@ericsson.com

[vince-fugnitto]

The changes work very well 👍 I'll add an explicit approval once the CQ I filed is approved.
I verified that:

• the Echo Theme command successfully displays the active theme kind using the activeColorTheme API
• the onDidChangeActiveColorTheme successfully fires when a theme is updated, and the message correctly displays.

[vince-fugnitto]

The CQ has been approved 👍

[vince-fugnitto]

I verified the changes once again and they work very well 👍

[paul-marechal]

Code LGTM, feature is working.