Fixes find widget shall be shown per split terminal

[jeanp413]

This PR fixes #145865

[meganrogge]

Thanks @jeanp413 for working on this. The code changes/clean-up look great 👍🏼

Github won't let me attach images or gifs ATM 😢

I notice a few things:

1. You have to focus a terminal for that find widget to become active. I think focusing a find widget should set the corresponding instance as the active one

2. When minding step 1, focusing terminal A and pressing enter in the find widget a few times results in the index 1 of 4 for example updating correctly ✅ . Leaving that find widget open and focusing terminal B and doing the same the results in the index being out of sync with the currently selected element. Investigating this issue as I implemented the index in xterm.js and could be a bug with that 😄

[jeanp413]

@meganrogge updated the PR, last commit is optional just some 💄 to match the findwidget behavior from a normal editor
Current behavior in stable:

[meganrogge]

great @jeanp413 thanks. I was just working on fixing the two problems I mentioned above and will revert my fix as yours looks better 👍🏼

[meganrogge]

Works great 😄

[Tyriar]

Works great, sorry about the delay 🙂