Add type-checking to `#[var(get, set)]` #4609

Job	Run time
license-guard	38s
unit-test	2m 29s
doc-lints	1m 13s
rustfmt	25s
clippy	1m 42s
godot-itest (linux-full)	4m 24s
godot-itest (linux-features-experimental)	4m 25s
godot-itest (linux-custom-api-json)	4m 7s
godot-itest (linux-4.4)	1m 42s
godot-itest (macos)	2m 39s
godot-itest (windows)	3m 2s
godot-itest (linux-release)	2m 57s
godot-itest (linux-4.3)	1m 10s
godot-itest (memcheck-dev-balanced)	4m 1s
godot-itest (memcheck-release-disengaged)	4m 0s
godot-itest (memcheck)	3m 36s
godot-itest (linux-4.2)	1m 6s
godot-itest (linux-4.5)	2m 17s
ci-status	9s
	46m 2s

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