struct improvement, part1: create more LCL_FLD (#48377)

* Add additional tests.

* Use LclFld when copy to/from promoted from/to an unpromoted struct/block.

* Response review.

Author: Sergey Andreenko

src/coreclr/jit/compiler.h

@@ -5890,6 +5890,8 @@ class Compiler
     GenTree* fgMorphSmpOpOptional(GenTreeOp* tree);
     GenTree* fgMorphConst(GenTree* tree);
 
+    bool fgMorphCanUseLclFldForCopy(unsigned lclNum1, unsigned lclNum2);
+
     GenTreeLclVar* fgMorphTryFoldObjAsLclVar(GenTreeObj* obj);
     GenTree* fgMorphCommutative(GenTreeOp* tree);