Break apart gtFoldExprConst into a couple functions so its more manageable (#128307)

This should be zero-diffs (minus a minor fix for 32-bit xarch) as it's
just taking the logic and splitting it out so we no longer have one
gigantic method. This helps make the code easier to read/browse and
should help the native compiler more easily inline the key paths in some
cases.

Doing this refactoring since I'm planning on moving some more folding
from morph into `gtFoldExpr` and this helps keep everything easy to
understand.

Author: tannergooding

src/coreclr/jit/compiler.h

@@ -3948,9 +3948,26 @@ class Compiler
     //-------------------------------------------------------------------------
 
     GenTree* gtFoldExpr(GenTree* tree);
+    GenTree* gtFoldExprConst(GenTree* tree);
+
     GenTree* gtFoldExprUnary(GenTreeUnOp* tree);
+    GenTree* gtFoldExprUnaryConst(GenTreeUnOp* tree);
+    GenTree* gtFoldExprUnaryConstInt(GenTreeUnOp* tree, GenTreeIntCon* intCon);
+    GenTree* gtFoldExprUnaryConstLng(GenTreeUnOp* tree, GenTreeIntConCommon* intConCommon);
+    GenTree* gtFoldExprUnaryConstDbl(GenTreeUnOp* tree, GenTreeDblCon* dblCon);
+
     GenTree* gtFoldExprBinary(GenTreeOp* tree);
-    GenTree* gtFoldExprConst(GenTree* tree);
+    GenTree* gtFoldExprBinaryConst(GenTreeOp* tree);
+    GenTree* gtFoldExprBinaryConstInt(GenTreeOp* tree, GenTreeIntCon* intCon1, GenTreeIntCon* intCon2);
+    GenTree* gtFoldExprBinaryConstLng(GenTreeOp* tree, GenTreeIntConCommon* intConCommon1, GenTreeIntConCommon* intConCommon2);
+    GenTree* gtFoldExprBinaryConstDbl(GenTreeOp* tree, GenTreeDblCon* dblCon1, GenTreeDblCon* dblCon2);
+
+    GenTree* gtBashTreeToConstInt(GenTree* tree, int32_t iconVal, FieldSeq* fieldSeq = nullptr);
+    GenTree* gtBashTreeToConstLng(GenTree* tree, int64_t lconVal, FieldSeq* fieldSeq = nullptr);
+    GenTree* gtBashTreeToConstDbl(GenTree* tree, double dconVal);
+
+    GenTree* gtFoldExprForOverflow(GenTree* tree);
+
     GenTree* gtFoldIndirConst(GenTreeIndir* indir);
     GenTree* gtFoldExprSpecial(GenTree* tree);
     GenTree* gtFoldExprSpecialFloating(GenTree* tree);