Support associated types in `#[godot_dyn]` #3189

Job	Run time
clippy	1m 18s
unit-test	1m 18s
doc-lints	50s
godot-itest (macos)	1m 11s
rustfmt	19s
godot-itest (windows)	1m 19s
godot-itest (linux-full)	1m 13s
license-guard	30s
run-examples	1m 16s
godot-itest (linux-features-experimental)	1m 14s
godot-itest (linux-4.1)	1m 14s
godot-itest (linux-4.2)	1m 5s
godot-itest (linux-memcheck)	1m 18s
ci-status	1s
	14m 6s

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