Merge #5480

5480: Fix snippetTextEdits applying to other files r=matklad a=TimoFreiberg

Fixes #4551
`vscode.window.visibleTextEditors` only contains editors whose contents are being displayed at the moment, so the previous logic only worked if the other file for which a snippetTextEdit is being received was visible in a separate split.

I feel that this is a hacky approach, so feel free to reject it for something nicer :)

Co-authored-by: Timo Freiberg <timo.freiberg@gmail.com>