[AArch64][GlobalISel] Better vecreduce.fadd lowering. (PR #73294)

This changes the fadd legalization to handle fp16 types, and treats more types
as legal so that the backend can produce the correct patterns. This is
currently a missing identity fold for `fadd x -0.0 -> x`
diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 6d5b876..3fa659e 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -2820,6 +2820,7 @@
     Observer.changedInstr(MI);
     return Legalized;
   }
+  case TargetOpcode::G_VECREDUCE_FADD:
   case TargetOpcode::G_VECREDUCE_FMIN:
   case TargetOpcode::G_VECREDUCE_FMAX:
   case TargetOpcode::G_VECREDUCE_FMINIMUM: