Refactor font rendering pipeline, remove `font-kit` and `pathfinder` #486

Job	Run time
test_all_features	1m 35s
msrv	31s
run_all_examples	2m 31s
cargo-doc	40s
build_and_test (macos-latest)	1m 45s
build_and_test (windows-latest)	2m 0s
build_and_test (ubuntu-latest)	1m 15s
	10m 17s

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