perf: dynamically dispatch context function in `WebIDLConverter` #3766

Job	Run time
compute-jobs	3s
build-linux / linux coverage	52s
build-linux / linux test-miri	51s
build-linux / linux lint-deps	52s
build-linux / linux test	50s
build-linux / linux lint	36s
build-linux / linux test-publish	51s
build-linux / linux test-ops	51s
build-linux / linux test-valgrind	19s
build-linux-arm / linux-arm test	42s
build-linux-arm / linux-arm test-miri	1s
build-linux-arm / linux-arm lint	1s
build-macos / macos lint	45s
build-macos / macos test	38s
build-windows / windows lint	41s
build-windows / windows test	43s
success	1s
	9m 37s

Provide feedback