Add back support for Godot 4.4

[dsnopek]

This is the next "godot-cpp v10" PR - it builds on top of:

• Generate GDExtension interface header and loader from JSON #1895
• Add api_version build option to select the API JSON file #1897

This one adds back support for Godot 4.4, and includes the extension_api.json for 4.4, such that you can build via scons api_version=4.4 out-of-the-box

Marked as DRAFT because it depends on the other "godot-cpp v10" PRs

[dsnopek]

The PRs that this one depended on are merged, so taking this out of DRAFT!

[Ivorforce]

I have to admit, I don't remember / can't comment on the changes from 4.4 to 4.5 at all.
But the code changes are simple enough, and it builds, so LGTM!