More Blk Op Refactoring

Code refactoring in preparation for 1st Class Structs:
Factor out the legacy code generation for CpObj.
Abstract some functionality to member methods.
Move some block-related method definitions.
Make fgOrderBlockOps legacy-only (it is unused in RyuJIT).
Factor out the code to create a block init value.
Add a new IsLocalExpr() method.
Change some variable names to distinguish between objects and their addresses.

Author: CarolEidt

src/jit/codegenclassic.h

@@ -314,6 +314,9 @@
                                                              regMaskTP  destReg,
                                                              regMaskTP  bestReg);
 
+    void                genCodeForCopyObj                   (GenTreePtr tree,
+                                                             regMaskTP  destReg);
+
     void                genCodeForBlkOp                     (GenTreePtr tree,
                                                              regMaskTP  destReg);