Make `xilem::Pod` more flexible (#806) #2598

Job	Run time
cargo check (msrv) (wasm32)	16s
cargo check (aarch64-android)	22s
cargo clippy (windows-latest)	4m 23s
cargo check (msrv) (windows-latest)	1m 53s
cargo clippy (macos-latest)	2m 40s
cargo clippy (wasm32)	1m 53s
cargo clippy (ubuntu-latest)	3m 15s
cargo doc	47s
cargo check (msrv) (macos-latest)	32s
formatting	35s
cargo check (msrv) (ubuntu-latest)	37s
Prime LFS Cache	7s
cargo test (wasm32)	24s
typos	4s
cargo test (windows-latest)	3m 15s
cargo test (macos-latest)	1m 49s
cargo test (ubuntu-latest)	4m 14s
	27m 6s

Provide feedback