[AArch64][GlobalISel] Expand handling for fptosi and fptoui (#70635)

Now that we have more types handled for zext/sext and trunc, it is
possible to get more types working for the vector float to integer
conversions. This patch adds fp16, widening and narrowing vector support
to handle more types. The smaller types wil be expanded to the size of
the larger element type. A couple of case require more awkward truncates
to get working as they go from illegal to illegal types.