Web: Catch using GDExtensions in a non-dlink build

[MarioLiebisch]

Previously, if one would try to use GDExtensions with a web build that doesn't have dynamic loading enabled, this would simply fail with a cryptic me.rtenv.loadDynamicLibrary is not a function error message.

If it's attempted again, it will now instead error out with GDExtension libraries are not supported by this engine version.

[akien-mga]

Would be good to provide information about:

• Having to enable "Extensions Support" in the export preset
• OR using custom built templates with dlink_enabled=yes

The UX is a bit awkward as "Extensions Support" I believe only toggles which of the official templates will be used, but if using custom built ones this logic doesn't apply.

[MarioLiebisch]

Should it even be an option? I'd say the editor should know there's an GDExtension somewhere, so it could pick it automatically or warn the user if there's no matching template. Maybe one could bundle an empty text file with the template to identify build options? Edit: The editor should be able to identify this already, just checking whether there's the "Side wasm" or not.

I mostly got into this situation by using a symbolic link from web_debug.zip to the new generated zip file. The export function still insisted on using web_debug.zip after all.

[dsnopek]

Discussed at the GDExtension meeting, and we agree that this PR is a good idea, but also agree with @akien-mga that the message should contain some information for the developer about what to do to fix the issue.

[MarioLiebisch]

Done. It will now read:

GDExtension libraries are not supported by this engine version. Enable "Extensions Support" for your export preset and/or build your custom template with "dlink_enabled=yes".

[dsnopek]

That message sounds good to me!

[akien-mga]

Thanks!