feat(webidl): distinguish Nullable from Option, allow setting default… #3742

Job	Run time
compute-jobs	2s
build-linux / linux coverage	6m 15s
build-linux / linux test	7m 30s
build-linux / linux lint	2m 27s
build-linux / linux lint-deps	1m 54s
build-linux / linux test-ops	8m 37s
build-linux / linux test-miri	7m 14s
build-linux / linux test-publish	1m 49s
build-linux / linux test-valgrind	23m 37s
build-linux-arm / linux-arm test	10m 58s
build-linux-arm / linux-arm test-miri	11m 14s
build-linux-arm / linux-arm lint	3m 27s
build-macos / macos lint	2m 13s
build-macos / macos test	6m 2s
build-windows / windows lint	6m 24s
build-windows / windows test	16m 7s
success	1s
	1h 55m 51s

Provide feedback