Refactor font rendering pipeline, remove `font-kit` and `pathfinder` #482

Job	Run time
msrv	32s
build_and_test (ubuntu-latest)	1m 29s
test_all_features	1m 3s
run_all_examples	2m 24s
cargo-doc	45s
build_and_test (windows-latest)	1m 18s
build_and_test (macos-latest)	1m 25s
	8m 56s

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