Support associated types in `#[godot_dyn]` #3221

Job	Run time
doc-lints	43s
godot-itest (macos)	55s
clippy	1m 45s
license-guard	31s
godot-itest (windows)	3m 5s
run-examples	1m 8s
rustfmt	15s
godot-itest (linux-full)	2m 40s
unit-test	2m 19s
godot-itest (linux-features-experimental)	1m 56s
godot-itest (linux-4.1)	1m 3s
godot-itest (linux-4.2)	1m 23s
godot-itest (linux-memcheck)	2m 7s
ci-status	1s
	19m 51s

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