Improve Scene Tree Dock's Node filter (Allow multiple terms & more)

[Mickeon]

This PR is a continuation of #65315, and a bit of a misnomer, because it actually does a whooping 3 things at once:

• Allows more than one term to be passed in the "Filter Node" search box, each term separated by spaces.💙

• Grays out any parent Node not matching the search, but still having to be there because a child does. This essentially (partially) supersedes Improve search filtering in scene tree editor #58481.

• To test the waters of this new implementation, and potentially expand upon the concept in the future (Add search filter syntax to the scene tree dock godot-proposals#4986):

  • Along with the already existing type: (Add a way to filter nodes by type in scene tree dock. #58377), adds a new group: filter. It matches any Node belonging to the passed group. If no argument is passed, it matches all Nodes belonging to any group. It also ignores groups used internally, and its alias is g.

Suppose we have this sample Scene:

" fl light "	"type:audio ju p"	"pe type:col"

Note that, and this is going to be in the test, ScaryObstacle1 and ScaryObstacle2 belong to the "enemy" group. ScarierObstacle belongs to the "enemy" and "horrifying" group.

"group:"	"group:horr"	"g:hor g:en"

Lastly, this implementation uses String.contains() over String.is_subsequence_of(). While the subsequence lead to "quicker typing", it also showed very inconsistent and unexpected results.

[Mickeon]

Notes for the future:

• I wanted to implement the search items expanding automatically if they match. It would've been as simple as a p_parent->set_collapsed(false);. But the main problem is, ironically, that all items would be expanded, even when the filtering stops, which is an outstanding annoyance. This means that, at the very least, the default, unfiltered state of the Tree's folding would have to be stored somewhere, but that's beyond the scope of this PR and can totally be done another time.

[Mickeon]

I had been waiting for the tags to show up all day at work! I'm really happy about this one.

[reduz]

Looks good, we should eventually find a way for the warning to be shown better than going to the toaster. Either text in red and a tooltip or a warning icon next to the line edit.

[akien-mga]

Thanks!