Text-editor context menu is too crowded

[bersbersbers]

• VSCode Version: 1.49.0
• OS Version: Win10

Steps to Reproduce:
I have been using VS Code for ~3 years now, and I have yet to reach a point where I can intuitively use the right-click context menu of the text editor. I have given up hope in a way.

1. Install a few common extensions (basically, Python, Gitlens)
2. Right-click in a .py file
3. That's too long:

Does this issue occur when all extensions are disabled?: No

[sbatten]

@joaomoreno for comments on submenu api

[joaomoreno]

Yeah, definitely needs cleanup. The submenu API will land stable this month. This needs effort both from core and extensions.

[alexdima]

I agree, but that is what happens when we open up a contribution point. Every extension believes that its actions are very important and must render in the context menu. IMHO this can be tackled by making the context menu editable by end users, e.g. similar to how keybindings can be edited by end users, to remove, to add, or to regroup actions in the context menu.

[jrieken]

/duplicate of #9285