Add project setting to change scene file casing

[Jummit]

Bugsquad edit: master version of #56909.

The documentation recommends file names to be in snake case, which is hard to implement because scene files take the name of the root node by default. This adds a project settings to change the default scene name to be either automatically generated, pascal case or snake case.

Should snake case be the default, like #47275 implemented?

Supersedes #47275

[Calinou]

Should snake case be the default, like #47275 implemented?

Yes, as it sidesteps the case sensitivity issues that many users run into when exporting projects from Windows or macOS.

[Jummit]

Should snake case be the default, like #47275 implemented?

Yes, as it sidesteps the case sensitivity issues that many users run into when exporting projects from Windows or macOS.

Done.

[fire]

Saw this was on the https://github.com/orgs/godotengine/projects/16 board and wasn't ready to be merged as is. Can you rebase?

[Jummit]

Saw this was on the github.com/orgs/godotengine/projects/16 board and wasn't ready to be merged as is. Can you rebase?

Done.

[Jummit]

@fire
CI is finally finished!

[fire]

While working on #56848.

I noticed there were special cases.

capitalize() before camelcase_to_underscore().
" " -> ""
"-" -> "_".

What are your thoughts?

[Jummit]

The first one was already there, I added the second one as well.

[akien-mga]

Approved in PR review meeting.

[akien-mga]

Thanks!

[rambda]

It seems that "Save Branch As Scene" naming is not affected by "editor/scene/scene_naming" in 4.0.beta1.

[KoBeWi]

It was fixed recently, will be available for beta2.