Add opened scenes list button

[arkology]

Attempt to resolve a problem raised in godotengine/godot-proposals#9954.

godot.windows.editor.dev.x86_64_8oll5CHTSk.mp4

Previous version, different dropdown icon (reverted after KoBeWi comment)

godot.windows.editor.dev.x86_64_VfAuMUlzC3.mp4

Closes godotengine/godot-proposals#9954

[arkology]

Interesting, in fork I don't have failed stylecheck action (https://github.com/arkology/godot/actions/runs/15944544374)
Upd: No edits in SVGs - no errors 😆

[KoBeWi]

I'm not sure if this needs a new icon, you can just use the GuiTabMenuHl.

[arkology]

I'm not sure if this needs a new icon, you can just use the GuiTabMenuHl.

Originally I used GuiTabMenuHl (you can see it in linked feature request issue), but then looked how it is done in other places like Notepad++ and Visual Studio.
If this is preferable, I'll revert it.

[seppoday]

I wonder if we need arrows now? I personally don't see myself using arrows when there is dropdown

[arkology]

I think still keeping them is ok because they indicate that there are invisible tabs.

[piotrtrkostrzewski94]

Hello, great idea, in my opinion a good extension of functionality would be to add a search engine, it would be useful when someone has so many scenes that entering the name will be faster for them. Theoretically it could be done using TextEdit, what do you think?

[arkology]

@piotrtrkostrzewski94 PopupMenu already has some kind of search functionality (https://docs.godotengine.org/en/stable/classes/class_popupmenu.html#class-popupmenu-property-allow-search).
More extended search functionality could be added in follow-up pr.

[piotrtrkostrzewski94]

@arkology Thank you very much