Chat - switch chat toolbar to use overlay widget

[Ladislau Szomoru (lszomoru)]

This pull request switches the chat session toolbar to use an overlay widget so that we can take advantage of stacking overlay widgets in the lower right hand corner in order to address the edge case in which both the chat session toolbar is being shown as well as the "editor content button" (ex: Resolve in Merge Editor). PR also contains a drive-by fix for stacking overlay widgets in the top/bottom right corners.

[Copilot]

Pull Request Overview

This PR switches the chat editing toolbar from absolute positioning within a container to using VS Code's overlay widget system. This provides better integration with the editor's layout and z-index management.

Key changes:

• Migrates chat toolbar from DOM container positioning to editor overlay widget
• Implements widget stacking system with ordinal values for proper layering
• Updates overlay widget positioning logic to support stacking for both top and bottom right corners

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/vs/workbench/contrib/chat/browser/chatEditing/chatEditingEditorOverlay.ts	Converts chat toolbar from absolute positioning to overlay widget with stack ordinal 1
src/vs/editor/contrib/floatingMenu/browser/floatingMenu.ts	Adds stack ordinal 2 to floating menu to ensure proper layering above chat toolbar
src/vs/editor/browser/viewParts/overlayWidgets/overlayWidgets.ts	Implements widget stacking logic for both top and bottom right corner positions

[Johannes Rieken (jrieken)]

I like the stacking but the reason for this not being an overlay widget (anymore) is that it should also work for notebooks. So, we would need to find a solution for that first

[Ladislau Szomoru (lszomoru)]

Johannes Rieken (@jrieken), that makes sense. I did not consider the notebook scenario.

[Ladislau Szomoru (lszomoru)]

Converting to draft to make sure that this does not get merged in its current form.