JIT: Fix gtGetClassHandle with commas

gtGetClassHandle has comments about "Tunnel through commas", yet several
of the cases then do not actually use the effective value, resulting in
possible asserts when this function is passed a comma.

Fixes an issue I saw in dotnet#87265 when morph invokes gtFoldTypeCompare for
the following IR:

```
fgMorphTree BB19, STMT00013 (before)
               [000045] -ACXG------                         *  JTRUE     void
               [000044] -ACXG------                         \--*  NE        int
               [000623] -ACXG------                            +--*  COMMA     ref
               [000622] DA---------                            |  +--*  STORE_LCL_VAR ref    V29 tmp18
               [000621] -----------                            |  |  \--*  LCL_FLD   ref    V07 loc3         [+0]
               [000041] -ACXG------                            |  \--*  CALL nullcheck ref    Microsoft.Extensions.Configuration.Test.ConfigurationProviderTestBase+TestKeyValue:get_AsArray():System.String[]:this
               [000620] -A--------- this                       |     \--*  COMMA     ref
               [000619] DA---------                            |        +--*  STORE_LCL_VAR ref    V30 tmp19
               [000618] -----------                            |        |  \--*  LCL_FLD   ref    V07 loc3         [+8]
               [000617] -----------                            |        \--*  LCL_VAR   ref    V30 tmp19
               [000043] -----------                            \--*  CNS_INT   ref    null
```

Author: jakobbotsch

src/coreclr/jit/gentree.cpp

@@ -17881,9 +17881,9 @@ CORINFO_CLASS_HANDLE Compiler::gtGetClassHandle(GenTree* tree, bool* pIsExact, b
 
         case GT_CNS_INT:
         {
-            if (tree->IsIconHandle(GTF_ICON_OBJ_HDL))
+            if (obj->IsIconHandle(GTF_ICON_OBJ_HDL))
             {
-                objClass = info.compCompHnd->getObjectType((CORINFO_OBJECT_HANDLE)tree->AsIntCon()->IconValue());
+                objClass = info.compCompHnd->getObjectType((CORINFO_OBJECT_HANDLE)obj->AsIntCon()->IconValue());
                 if (objClass != NO_CLASS_HANDLE)
                 {
                     // if we managed to get a class handle it's definitely not null
@@ -17898,14 +17898,14 @@ CORINFO_CLASS_HANDLE Compiler::gtGetClassHandle(GenTree* tree, bool* pIsExact, b
         {
             // If we see a RET_EXPR, recurse through to examine the
             // return value expression.
-            GenTree* retExpr = tree->AsRetExpr()->gtInlineCandidate;
+            GenTree* retExpr = obj->AsRetExpr()->gtInlineCandidate;
             objClass         = gtGetClassHandle(retExpr, pIsExact, pIsNonNull);
             break;
         }
 
         case GT_CALL:
         {
-            GenTreeCall* call = tree->AsCall();
+            GenTreeCall* call = obj->AsCall();
             if (call->gtCallMoreFlags & GTF_CALL_M_SPECIAL_INTRINSIC)
             {
                 NamedIntrinsic ni = lookupNamedIntrinsic(call->gtCallMethHnd);