internal-fn: Fix vector extraction into promoted subreg.

internal-fn: Fix vector extraction into promoted subreg.

This patch fixes the case where vec_extract gets passed a promoted
subreg (e.g. from a return value).  This is achieved by using
expand_convert_optab_fn instead of a separate expander function.

gcc/ChangeLog:

	* internal-fn.cc (vec_extract_direct): Change type argument
	numbers.
	(expand_vec_extract_optab_fn): Call convert_optab_fn.
	(direct_vec_extract_optab_supported_p): Use
	convert_optab_supported_p.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/vls-vlmax/vec_extract-1u.c: New test.
	* gcc.target/riscv/rvv/autovec/vls-vlmax/vec_extract-2u.c: New test.
	* gcc.target/riscv/rvv/autovec/vls-vlmax/vec_extract-3u.c: New test.
	* gcc.target/riscv/rvv/autovec/vls-vlmax/vec_extract-4u.c: New test.
	* gcc.target/riscv/rvv/autovec/vls-vlmax/vec_extract-runu.c: New test.

(cherry picked from commit c94e0f52f40310b6faeae11bae3366ccb1435199)