masonry: reimplement `Widget::get_child_at_pos` (#565) #1619

Job	Run time
cargo check (msrv) (wasm32)	21s
cargo check (msrv) (windows-latest)	1m 14s
cargo check (aarch64-android)	19s
cargo clippy (windows-latest)	3m 13s
cargo check (msrv) (macos-latest)	27s
cargo clippy (macos-latest)	1m 8s
cargo check (msrv) (ubuntu-latest)	31s
cargo clippy (wasm32)	1m 19s
cargo doc	1m 21s
cargo clippy (ubuntu-latest)	1m 42s
formatting	33s
Prime LFS Cache	3s
cargo test (wasm32)	20s
typos	10s
cargo test (windows-latest)	3m 14s
cargo test (macos-latest)	1m 30s
cargo test (ubuntu-latest)	4m 44s
	22m 9s

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