Fix dotnet/coreclr#7093

Fix dotnet/coreclr#7093

This is an assert due to how STRESS_64RSLT_MUL is implemented. This
stress mode converts:
```
/--*  lclVar    int    V01 loc0
*  *         int
\--*  lclVar    int    V01 loc0
```
to:
```
*  cast      int <- long
|  /--*  cast      long <- int
|  |  \--*  lclVar    int    V01 loc0
\--*  *         long
   \--*  cast      long <- long
      \--*  nop       long
         \--*  lclVar    int    V01 loc0
```
Thus, the long 'nop' node is above an 'int' operand node. This led to an assert
in genCodeForTreeLng() that the lclVar was type long, which is isn't.

I added yet another cast under the 'nop' to fix this typing problem:
```
*  cast      int <- long
|  /--*  cast      long <- int
|  |  \--*  lclVar    int    V01 loc0
\--*  *         long
   \--*  cast      long <- long
      \--*  nop       long
         \--*  cast      long <- int
            \--*  lclVar    int    V01 loc0
```

Commit migrated from https://github.com/dotnet/coreclr/commit/c16b6bc96c1aa1edd9a3085a12f12a9df4169da5