[GISel] Add new combines for G_FMINNUM/MAXNUM and G_FMINIMUM/MAXIMUM

I noticed https://reviews.llvm.org/D87415 added SDAG combines to fold
FMIN/MAX instrs with NaNs.

The patch implements the same NaN combines for GISel GMIR FMIN/MAX opcodes:
G_FMINNUM(X, NaN) -> X
G_FMAXNUM(X, NaN) -> X
G_FMINIMUM(X, NaN) -> NaN
G_FMAXIMUM(X, NaN) -> NaN

The patch adds AArch64 tests for these combines as well.

Reviewed by: arsenm

Differential revision: https://reviews.llvm.org/D125819