Add support for developing Blender 4.2 extensions as well as legacy addons

[strike-digital]

This adds support for automatically detecting whether an addon is an extension, and if it is, installing as one instead of as a legacy addon.

Main changes:

• If an addon has a top level blender_manifest.toml file, it is treated as an extension (in supported blender versions).
• If so, the python code creates the symlink in the extensions' directory, and prepends bl_ext.user_default. to the module name.
• Reloading an addon now also passes the list of addon source directories so that the python code can determine whether each one is an extension.
• Small refactor to the python startup script to use a dataclass to pass the addons_to_load rather than a tuple, makes it easier to know what info is available (could be reverted if it doesn't fit).

If an addon is not an extension, or if the Blender version is lower than 4.2, it will just be treated as a normal addon.

[JacquesLucke]

Would you be interested in improving the experience for creating a new Blender extension? Maybe it's as simple as adding a new entry in getNewAddonGenerator with a new template (+ maybe rename the existing templates). Maybe the auto-load functionality has to be improved for Blender 4.2 too.

https://twitter.com/CGSebSciFi/status/1800505001036730668

[strike-digital]

Yeah, definitely, I'll give that a shot 👍

[strike-digital]

Oh also, I was wondering about auto formatting the python code? Currently, it doesn't comply with PEP8 at all, and my editor likes to complain about it. I'd probably use black with default settings, except for a longer line limit, as it's pretty standardised.

If I open another pull request for it, is it likely to get merged?

[JacquesLucke]

I'm fine with improving the formatting. Using black seems ok. Ideally, the code is simplified so far that it is formatted the same by different formatters, but it's nice to be consistent with at least one popular one.

[strike-digital]

Hi, I saw you sent a message about creating a release, but the notification disappeared from windows and I can't seem to find it on the website. Every day the urge to move to linux grows stronger😅

From what I saw, it was whether I was going to make any more pull requests before the extension should be released? In that case, I was just going to make one for the formatting, but since that shouldn't change any functionality it should be ok?

[JacquesLucke]

I sent it as a private message on Blender Chat. You should be able to see it there, but thx for letting me know here.

[strike-digital]

Ah that explains it, thanks!