Refactor the function

Split it into specialized variants for each operator,
delete redundant code, fix up one case of wrong typing
for a constant in the MUL -> SHIFT optimization.

One CSE diff due to different VNs because of the typing
change for the constant (int -> long).

Many text diffs: "mov x3, 5" => "mov w3, 5".

Author: SingleAccretion

src/coreclr/jit/compiler.h

@@ -6406,6 +6406,9 @@ class Compiler
     GenTree* fgOptimizeEqualityComparisonWithConst(GenTreeOp* cmp);
     GenTree* fgOptimizeRelationalComparisonWithConst(GenTreeOp* cmp);
     GenTree* fgOptimizeCommutativeArithmetic(GenTreeOp* tree);
+    GenTree* fgOptimizeAddition(GenTreeOp* add);
+    GenTree* fgOptimizeMultiply(GenTreeOp* mul);
+    GenTree* fgOptimizeBitwiseAnd(GenTreeOp* andOp);
     GenTree* fgPropagateCommaThrow(GenTree* parent, GenTreeOp* commaThrow, GenTreeFlags precedingSideEffects);
     GenTree* fgMorphRetInd(GenTreeUnOp* tree);
     GenTree* fgMorphModToSubMulDiv(GenTreeOp* tree);