Search result navigation with next and previous focus

[shynxe]

What it does

Implementation for issue: #12692

Added commands for Search: Focus Next Search Result and Search: Focus Previous Search Result, similar to their VSCode counterparts, along with the corresponding keybinds.

How to test

1. Run Theia.
2. Search using terms which return multiple results.
3. Use the command palette (Ctrl+Shift+P) and enter Search: Focus Next Search Result (or its Previous counterpart) or using the F4 / Shift+F4 keybinds.
4. Notice how the results are focused correspondingly.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[msujew]

@shynxe Thank you for your contribution. FYI we already have a PR on this issue (though it wasn't linked), see #12703. We'll need to see which one we'll continue to review/merge.

[shynxe]

@shynxe Thank you for your contribution. FYI we already have a PR on this issue (though it wasn't linked), see #12703. We'll need to see which one we'll continue to review/merge.

I just noticed that now while I was scrolling through other PRs. Fortunately, this solution is not completely useless, as it covers edge cases which the other one doesn't, such as automatically expanding the FileNode of the focused LineNode in the results view.

[vince-fugnitto]

@shynxe thank you for taking the time to contribute! We'll go ahead with #12703 for the time being and update it as needed since it is still under review. There are a couple of issues with this implementation at the moment and reviewing the same feature in multiple pull-requests takes time. Thank you for understanding!