Add a few vscode menu contribution points

[jonah-iden]

What it does

implements parts of #13051 specificly:

• extension/context
• terminal/context
• terminal/title/context

since Theias terminals are there own tabs, the last contribution is implemented when right clicking on the tab title. The others should be at the same place they are in vscode

How to test

Here is a test extension (inlucluding vsix) which adds a menu entry to all of theias missing contribution points.

extension/context can be found when clicking the cog wheel (or right clicking) on an extension in the Extension widget terminal/context can be found when right clicking inside a terminal terminal/title/context can be found when right clicking the tab title of a terminal

im not too happy with having the menu path ['extensions_context_menu', '3_contribution'] duplicated. If you have an idea where to place the constant for this i'd be happy to implement it.

Follow-ups

Review checklist

• [x] 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

[rschnekenbu]

I would be happy to help for review here