This is needed to avoid aborting due to missing mscorlib for projects that do not use C#.
If 'res://.mono/' exists, then we assume the project uses C#, in which case a missing mscorlib should still abort.
Only possible if the object class is a "native type". If the object class is a user class (that derives a "native type") then a script is needed.
Since CSharpLanguage does cleanup of script instance bindings when finished, cases like #25621 will no longer cause problems.
Fixed ~Object() trying to free script instance bindings after the language has already been removed, which would result in a NULL dereference.
Previously this was only done when building the script for running the game. This was a problem because the user could want to build the project manually with the "Build project" button, to then run the game from the command line or similar.
Avoid CSharpInstance from accessing its state after self destructing (by deleting the Reference owner).
It's now safe to replace the script instance without leaking or crashing.
Also fixed godot_icall_Object_weakref return reference being freed before returning.
To help users writing good cross-platform code, Godot's
`FileAccessWindows:open()` will issue a warning on case mismatch, which
happens here with capitalized extensions given by `PATHEXT` compared to
actual file extensions which are lowercase 99% of the time.
Fixes#25368.
BaseIntermediateOutputPath seems to be empty by default. The workaround is to explicitly set it.
Also fixed passing char instead of char[] to String.Split. Why was this even working with Mono?
Some used 'is_valid()' checks, others not. Validity is already checked in 'unref()',
and 'remove_resource_format_*()' has an ERR_FAIL condition on 'is_null()' already
(which shouldn't happen since we're only unregistering things that we previously
registered.
Also add missing GDCLASS statement in ResourceFormatLoaderVideoStreamGDNative,
missed in #20552 which was last amended before #19501 was merged.
During reloading in `GDScriptLanguage::reload_all_scripts` a placeholder instance that must remain so is replaced with a new placeholder instance. The state is then restored by calling `ScriptInstance::set` for each property. This does not work if the script is missing the properties due to build/parse failing.
The fix for such cases is to call `placeholder_set_fallback` instead of `set` on the script instance.
I took this chance to move the `build_failed` flag from `PlaceHolderScriptInstance` to `Script`. That improves the code a lot. I also renamed it to `placeholder_fallback_enabled` which is a much better name (`build_failed` could lead to misunderstandings).
