Make StyleProperty::FontStack more ergonomic. #358

Job	Run time
cargo clippy (android) (armv7-linux-androideabi)	1m 57s
cargo check (msrv) (android) (armv7-linux-androideabi)	26s
cargo clippy (android) (aarch64-linux-android)	1m 55s
cargo check (msrv) (windows-latest)	1m 24s
cargo check (msrv) (android) (aarch64-linux-android)	57s
cargo clippy (windows-latest)	4m 58s
cargo clippy (android) (x86_64-linux-android)	1m 53s
cargo check (msrv) (macos-latest)	27s
cargo check (msrv) (android) (x86_64-linux-android)	57s
cargo clippy (macos-latest)	1m 58s
cargo check (msrv) (ubuntu-latest)	33s
cargo clippy (ubuntu-latest)	2m 26s
cargo doc (windows-latest)	1m 34s
cargo fmt	21s
cargo doc (macos-latest)	31s
cargo test (windows-latest)	1m 43s
typos	4s
cargo doc (ubuntu-latest)	26s
cargo test (macos-latest)	29s
cargo test (ubuntu-latest)	26s
	25m 25s

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