Find widget shall be shown per split terminal

[sandy081]

Testing #145629

Find widget is shown for all split terminals which makes it confusing where I am searching. For eg., in above screenshot the wrong terminal is highlighting find results which is not matched with with text in find widget.

[meganrogge]

@Tyriar What's the historical context for this decision?

[Tyriar]

I think it's just the find widget was added before splits. It would make sense to do this especially now considering we needed to reimplement parts of find inside the terminal editor; it'd be easier if it was encapsulated inside TerminalInstance or XtermTerminal.

[jeanp413]

Created PR #155361 fixing this