Refactor font rendering pipeline, remove `font-kit` and `pathfinder` #501

Job	Run time
test_all_features_exclude_doctests	1m 3s
test_all_features_exclude_ab_glyph	1m 25s
msrv	41s
build_and_test (ubuntu-latest)	1m 25s
build_and_test (macos-latest)	1m 22s
cargo-doc	36s
run_all_examples	2m 18s
build_and_test (windows-latest)	3m 6s
	11m 56s

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