Set of GUI2 widgets fixes

[farmaazon]

Pull Request Description

Implements first two points of #8745

1. The fix for drop-down was simple, just stop click propagation
2. The fix for connections was much more complicated. It turned out, that it's about keeping track of hovered ports; when picking an option in WidgetSelection makes the drop-down disappear - but that won't emit pointerleave event, so the port was still deemed hovered. Changed the mechanism for tracking hovered port to more "centralized" one.

Important Notes

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• All code has been tested:
  • Unit tests have been written where possible.
  • If GUI codebase was changed, the GUI was tested when built using ./run ide build.