Make StyleProperty::FontStack more ergonomic. #359

Job	Run time
cargo check (msrv) (android) (armv7-linux-androideabi)	35s
cargo clippy (windows-latest)	24s
cargo clippy (android) (armv7-linux-androideabi)	56s
cargo check (msrv) (android) (aarch64-linux-android)	58s
cargo clippy (macos-latest)	29s
cargo check (msrv) (windows-latest)	1m 9s
cargo clippy (android) (aarch64-linux-android)	38s
cargo clippy (ubuntu-latest)	24s
cargo check (msrv) (macos-latest)	27s
cargo check (msrv) (android) (x86_64-linux-android)	49s
cargo clippy (android) (x86_64-linux-android)	54s
cargo check (msrv) (ubuntu-latest)	28s
cargo doc (windows-latest)	1m 42s
cargo fmt	25s
cargo doc (macos-latest)	24s
cargo doc (ubuntu-latest)	23s
cargo test (windows-latest)	26s
typos	4s
cargo test (macos-latest)	25s
cargo test (ubuntu-latest)	27s
	12m 27s

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