Enable multireg returns on Arm64

Added method IsMultiRegPassedType and updated IsMultiRegReturnType
Switched these methods to using getArgTypeForStruct and getReturnTypeForStruct
Removed IsRegisterPassable and used IsMultiRegReturned instead.
Converted lvIsMultiregStruct to use getArgTypeForStruct
Renamed varDsc->lvIsMultiregStruct() to compiler->lvaIsMultiregStruct(varDsc)
Skip calling getPrimitiveTypeForStruct when we have a struct larger than 8 bytes
Refactored ReturnTypeDesc::InitializeReturnType
Fixed missing SPK_ByReference case in InitializeReturnType
Fixes for RyiJIt x86 TYP_LONG return types and additional ARM64 work for full multireg support
Added ARM64 guard the uses of MAX_RET_MULTIREG_BYTES with FEATURE_MULTIREG_RET
Fixes for multireg returns in Arm64 Codegen
Added dumping of lvIsMultiRegArg and lvIsMultiRegRet in the assembly output
Added check and set of compFloatingPointUsed to InitializeStructReturnType
Fixes to handle JIT helper calls that say they return a TYP_STRUCT with no class handle available
Placed all of the second GC return reg under MULTIREG_HAS_SECOND_GC_RET ifdefs
Added the Arm64 VM changes from Rahul's PR 5175
Update getArgTypeForStruct for x86/arm32 so that it returns TYP_STRUCT for all pass by value cases
Fixes for the passing of 3,5,6 or 7 byte sized structs
Fix issue on ARM64 where we would back fill into x7 after passing a 16-byte struct on the stack
Implemented register shuffling for multi reg Call returns on Arm64
Fixed regression on Arm32 for struct args that are not multi regs
Updated Tests.Lst with 23 additional passing tests

Changes from codereview feedback

Author: briansull

src/jit/codegen.h

@@ -443,26 +443,26 @@ protected :
 
     void                genPrologPadForReJit();
 
-    void                genEmitCall(int                                                 callType,
-                                    CORINFO_METHOD_HANDLE                               methHnd,
-                                    INDEBUG_LDISASM_COMMA(CORINFO_SIG_INFO*             sigInfo)
-                                    void*                                               addr
-                                    X86_ARG(ssize_t                                     argSize),
-                                    emitAttr                                            retSize
-                                    FEATURE_UNIX_AMD64_STRUCT_PASSING_ONLY_ARG(emitAttr secondRetSize),
-                                    IL_OFFSETX                                          ilOffset,
-                                    regNumber                                           base   = REG_NA,
-                                    bool                                                isJump = false,
-                                    bool                                                isNoGC = false);
+    void                genEmitCall(int                                           callType,
+                                    CORINFO_METHOD_HANDLE                         methHnd,
+                                    INDEBUG_LDISASM_COMMA(CORINFO_SIG_INFO*       sigInfo)
+                                    void*                                         addr
+                                    X86_ARG(ssize_t                               argSize),
+                                    emitAttr                                      retSize
+                                    MULTIREG_HAS_SECOND_GC_RET_ONLY_ARG(emitAttr  secondRetSize),
+                                    IL_OFFSETX                                    ilOffset,
+                                    regNumber                                     base   = REG_NA,
+                                    bool                                          isJump = false,
+                                    bool                                          isNoGC = false);
 
-    void                genEmitCall(int                   callType, 
-                                    CORINFO_METHOD_HANDLE methHnd,
-                                    INDEBUG_LDISASM_COMMA(CORINFO_SIG_INFO* sigInfo)
-                                    GenTreeIndir*         indir
-                                    X86_ARG(ssize_t       argSize),
-                                    emitAttr              retSize
-                                    FEATURE_UNIX_AMD64_STRUCT_PASSING_ONLY_ARG(emitAttr secondRetSize),
-                                    IL_OFFSETX            ilOffset);
+    void                genEmitCall(int                                           callType, 
+                                    CORINFO_METHOD_HANDLE                         methHnd,
+                                    INDEBUG_LDISASM_COMMA(CORINFO_SIG_INFO*       sigInfo)
+                                    GenTreeIndir*                                 indir
+                                    X86_ARG(ssize_t                               argSize),
+                                    emitAttr                                      retSize
+                                    MULTIREG_HAS_SECOND_GC_RET_ONLY_ARG(emitAttr  secondRetSize),
+                                    IL_OFFSETX                                    ilOffset);
 
 
     //
@@ -900,7 +900,7 @@ public :
     void                instEmit_indCall(GenTreePtr     call,
                                          size_t         argSize,
                                          emitAttr       retSize
-                                         FEATURE_UNIX_AMD64_STRUCT_PASSING_ONLY_ARG(emitAttr    secondRetSize));
+                                         MULTIREG_HAS_SECOND_GC_RET_ONLY_ARG(emitAttr  secondRetSize));
 
     void                instEmit_RM     (instruction    ins,
                                          GenTreePtr     tree,