Support associated types in `#[godot_dyn]` #3216

Job	Run time
doc-lints	52s
clippy	1m 42s
rustfmt	19s
godot-itest (macos)	56s
license-guard	31s
godot-itest (windows)	2m 49s
run-examples	1m 19s
godot-itest (linux-full)	2m 19s
unit-test	2m 21s
godot-itest (linux-features-experimental)	1m 53s
godot-itest (linux-4.1)	1m 18s
godot-itest (linux-4.2)	1m 4s
godot-itest (linux-memcheck)	2m 30s
ci-status	1s
	19m 54s

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