aarch64: Add testcase for vectorconvert lowering [PR110473]

aarch64: Add testcase for vectorconvert lowering [PR110473]

Vectorconvert lowering was changed to use the convert optab directly
starting in r15-1677-gc320a7efcd35ba. I had filed an aarch64 specific
issue for this specific thing and it would make sense to add an aarch64
specific testcase instead of just having a x86_64 specific ones for
this.

Pushed as obvious after testing for aarch64-linux-gnu.

	PR tree-optimization/110473
	PR tree-optimization/107432

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/vect-convert-1.c: New test.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>