[AArch64][SVE] Duplicate FP_EXTEND/FP_TRUNC -> LOAD/STORE dag combines

By duplicating these dag combines we can bypass the legality checks that
they do, this allows us to perform these combines on larger than legal
fixed types, which in turn allows us to bring the same benefits D114580
brought but to larger than legal fixed types.

Depends on D114580

Differential Revision: https://reviews.llvm.org/D114628