Hide query editor action buttons when in diff editor

[caohai]

This PR fixes #18559
Currently we show query editor action buttons in the diff editor which is not relevant. This bumps the diff-related actions into .... This PR adds an isInDiffEditor check during the action button contribution to hide them when the editor is in diff view. This change works for diff views originated from both git diff and the manual Select for Compare operation.

Before:

After:

VSCode doc for isInDiffEditor flag:
https://code.visualstudio.com/api/references/when-clause-contexts#:~:text=editorLangId%20%3D%3D%20typescript%22.-,isInDiffEditor,-The%20active%20editor

[github-actions]

PR Changes

Category	Main Branch	PR Branch	Difference
Code Coverage	50.38%	50.53%	$${\color{lightgreen} .15\% }$$
VSIX Size	12136 KB	12160 KB	$${\color{lightgreen} 24 KB \space (0\%) }$$
Webview Bundle Size	3180 KB	3180 KB	$${\color{lightgreen} 0 KB \space (0\%) }$$

[kburtram]

lgtm