Add separate feature tags for editor runtime

[KoBeWi]

This PR adds 2 new feature tags: editor_hint and editor_runtime. The former is used in the editor, the latter in running project. Both are only available in editor builds.
editor feature tag stays as is, for compatibility reasons and for consistency with template. Documentation will need updating after this is merged.

EDIT:

• Fixes Boot splash image is also used when Godot editor starts #22073 You can override splash image for editor_hint.
• Fixes Changing the tooltip delay in project settings affects the editor #9030
• Fixes Allow changing of Editor tooltip delay #27879
• Supersedes Add a tooltip delay setting for editor #35806

[RandomShaper]

Per the Godot jargon, it would have to be tools*_, but maybe that's not very user-friendly. Moreover, shouldn't editor already be used only for the editor itself vs. tools-enabled builds?

[Calinou]

editor_main is up to discussion tbh, I couldn't come up with a better word.

Out of curiosity, why not editor_hint for consistency with is_editor_hint()? The downside is that this term is a bit more obscure to people not used to writing @tool scripts, but it should be immediately obvious for people who've written one.

[Calinou]

This changes behavior a little since the project running from the editor will now keep the screen on (this may or may not be desired, especially on a laptop on battery). Just noting this for the future.

[KoBeWi]

I think the previous behavior was not really intended; it came from a limitation.

[akien-mga]

I wonder if we shouldn't have just editor and editor_runtime (so keep using editor for what is now editor_hint in this PR).

This would slightly break compat on the behavior of editor, but IMO the current behavior is confusing, and the two new feature tags make it worse as it's not obvious to users what's the difference between editor and editor_hint/editor_runtime.

[KoBeWi]

editor is useful for any code that's supposed to run only in editor build, so that the code does not accidentally slip to exported project, thus making it closer to editor_runtime. From my experience at least, idk how other people use it.

[akien-mga]

I guess one could use debug for that? But yeah, I guess it still makes sense to have a feature that matches target=editor specifically. The names are just a bit confusing.

I'm not too fond of editor_hint specifically, though I know that's what we have in Engine. I guess it's the best we can do for now :)

[KoBeWi]

I guess one could use debug for that?

Unless they ship game using debug build (which can happen sometimes ;)

[akien-mga]

Thanks!