Only update EditorSceneTabs tabs when necessary

[kitbdev]

Fixes resizing rebuilds all tabs
Fixes updating scene unsaved state (basically every action) rebuilds all tabs
Fixes #81513
Fixes this TODO in editor_scene_tabs

// TODO: This REALLY should be done in a better way than replacing all tabs after almost EVERY action.

update_scene_tabs now resizes its tabs only if it needs to, instead of always clearing and adding one by one.
added _update_tab_titles - updates the titles and icons of tabs. If the tab already has those values, it will not redraw.
added _scene_tabs_resized - repositions the add button. Used when resizing.

This could be optimized further by updating only the affected tab.

Needs testing on Mac to make sure the global menu works as expected. Particularly that it updates its name based on saved/unsaved state and that reordering tabs doesn't break it.

[KoBeWi]

Did some quick testing and seems to work correctly

[kitbdev]

updated to use set_block_signals and moved an if statement out of a for loop.

[YuriSizov]

Looks pretty great! Some lines related to global menus could probably be spread across multiple lines for readability, but that's not important right now.

[YuriSizov]

Thanks!