Add vector pair builtin tests; Optimize extract vector from memory.

Add vector pair builtin tests; Optimize extract vector from memory.

2023-08-31  Michael Meissner  <meissner@linux.ibm.com>

gcc/

	* config/rs6000/vector-pair.md (vpair_get_vector_<vp_pmode>_mem): New
	insn.

gcc/testsuite/

	* gcc.target/powerpc/vector-pair-01.c: New test.
	* gcc.target/powerpc/vector-pair-02.c: New test.
	* gcc.target/powerpc/vector-pair-03.c: New test.
	* gcc.target/powerpc/vector-pair-03.c: New test.