`ColorStopsSource::collect_stops` now consumes `self` #283

Job	Run time
cargo clippy (wasm32)	28s
cargo check (msrv) (windows-latest)	35s
cargo clippy (windows-latest)	50s
cargo check (msrv) (wasm32)	30s
cargo check (msrv) (macos-latest)	30s
cargo clippy (macos-latest)	29s
cargo doc	16s
formatting	25s
cargo check (msrv) (ubuntu-latest)	37s
cargo test (windows-latest)	45s
cargo clippy (ubuntu-latest)	23s
cargo test (wasm32)	17s
cargo test (macos-latest)	20s
typos	4s
cargo test (ubuntu-latest)	15s
	6m 44s

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