Fix IMGREL32 static field addr value-num blindspot

When `fgMorphField` lowers a static field reference for which
`eeGetRelocTypeHint` returns `IMAGE_REL_BASED_REL32`, it creates an
`IntCon`, flagged with `GFT_ICON_STATIC_HDL` and marked with the static
field in its `gtFieldSeq` field, to represent the field's address (as
opposed to the normal case where it generates a `ClsVar`).  This change
updates the `IsFieldAddr` helper used by value-numbering/loop-hoisting to
recognize such constants as the appropriate field address, which then
allows the disambiguation/tracking of accesses to these fields to kick in
as it does for `ClsVar` nodes.

Fixes #6900.

src/jit/gentree.cpp

@@ -15275,19 +15275,23 @@ bool GenTree::IsFieldAddr(Compiler* comp, GenTreePtr* pObj, GenTreePtr* pStatic,
             baseAddr  = gtOp.gtOp1;
         }
     }
+    // Check if "this" has a zero-offset annotation.
+    else if (comp->GetZeroOffsetFieldMap()->Lookup(this, &newFldSeq))
+    {
+        baseAddr = this;
+        mustBeStatic = true;
+    }
+    else if (OperGet() == GT_CNS_INT && gtIntCon.gtFieldSeq != nullptr)
+    {
+        // Address is a literal constant; must be a static field.
+        newFldSeq = gtIntCon.gtFieldSeq;
+        baseAddr = this;
+        mustBeStatic = true;
+    }
     else
     {
-        // Check if "this" has a zero-offset annotation.
-        if (!comp->GetZeroOffsetFieldMap()->Lookup(this, &newFldSeq))
-        {
-            // If not, this is not a field address.
-            return false;
-        }
-        else
-        {
-            baseAddr     = this;
-            mustBeStatic = true;
-        }
+        // This is not a field address.
+        return false;
     }
 
     // If not we don't have a field seq, it's not a field address.