Made "Show Node in Tree" button more user friendly

[Xenoparrot]

This PR is just building on the great PR #75274. The goal was to improve useability, mostly for the "Show Node in Tree" button.

The changes fix the following issues:

• Dragging and reparenting can now be done more seamlessly.
  • This was harder before due to multiselecting the referenced node with the edited node
• The scene tree dock is now focused if it was not focused when the button is pressed, consistent with pressing the “Show in Filesystem” button on exported resources.
• Pressing the button on multiple properties no longer creates a big glob of selected nodes in the SceneTreeDock.
• Right clicking the assign button now pulls up the little menu, consistent with exported resources.

I acknowledge that the changes may be a little hacky or wrong. I’ve never done this before. Though I mostly just copied code from around the source to avoid making obvious mistakes, so they should be fewer.

I initially intended to make some suggestions on the original PR, but it was merged faster than I expected, so I missed my opportunity.

Here is how it looks in action:

no big glob of multiselect
https://github.com/godotengine/godot/assets/92269209/76618fb1-bc18-4156-bbea-b634f6b4ba27

right clicking works
https://github.com/godotengine/godot/assets/92269209/374e3287-6eea-407a-b81a-e5d7daac4abe

dragging works instantly because of not using multiselect
https://github.com/godotengine/godot/assets/92269209/442066bf-e022-48fb-b5c4-93c681dd4771

tab switches if you don't already have SceneTreeDock open
https://github.com/godotengine/godot/assets/92269209/00366491-022e-4bf1-b38a-c2b2352a7c90

This change does affect the way the node looks when shown in tree (it's a lot more subtle now), but I thought it was a worthwhile sacrifice for making dragging easier and not making multiselect globs. I'll remove it if I'm the only one who thinks so.