aarch64: Remove redundant zeroing/merging in SVE intrinsics [PR106326]

aarch64: Remove redundant zeroing/merging in SVE intrinsics [PR106326]

Many predicated SVE intrinsics provide three forms of predication:
zeroing, merging, and any/dont-care.  All three are equivalent when
the predicate is all-true, so this patch drops the zeroing and
merging in that case.

gcc/
	PR target/106326
	* config/aarch64/aarch64-sve-builtins.h (is_ptrue): Declare.
	* config/aarch64/aarch64-sve-builtins.cc (is_ptrue): New function.
	(gimple_folder::redirect_pred_x): Likewise.
	(gimple_folder::fold): Use it.

gcc/testsuite/
	PR target/106326
	* gcc.target/aarch64/sve/acle/general/pr106326_1.c: New test.