MATCH: Optimize `VEC_SHL_INSERT (dup (A), A)` to just `dup (A) [PR116075]

MATCH: Optimize `VEC_SHL_INSERT (dup (A), A)` to just `dup (A) [PR116075]

It was noticed if we have `.VEC_SHL_INSERT ({ 0, ... }, 0)` it was not being
simplified to just `{ 0, ... }`. This was generated from the autovectorizer
(maybe even on accident, see PR tree-optmization/116081).

This adds a few SVE testcases to see if this is optimized since the
auto-vectorizer or intrinsics are the only two ways of getting this
produced.

Changes since:
* v1: Move the constant case over to fold-const-call.cc.
      Simplify match pattern to use handle vec_duplicate.

Build and tested for aarch64-linux-gnu with no regressions.

	PR target/116075

gcc/ChangeLog:

	* fold-const-call.cc (fold_const_vec_shl_insert): New function.
	(fold_const_call): Call fold_const_vec_shl_insert for CFN_VEC_SHL_INSERT.
	* match.pd (`VEC_SHL_INSERT (dup (A), A)`): New pattern.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/sve/dup-insr-1.c: New test.
	* gcc.target/aarch64/sve/dup-insr-2.c: New test.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>