[mono] Simplify of OffsetToStringData as it's done on coreclr (dotnet#93987)

* Change implementation of OffsetToStringData as it's done on coreclr

* Fix comment

* Remove more comments

* completely remove the comments

* Update RuntimeHelpers.Mono.cs

* Addressing comments

* Addressing @lambdageek comment.

Author: thaystg

src/mono/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeHelpers.Mono.cs

@@ -30,11 +30,7 @@ public static void InitializeArray(Array array, RuntimeFieldHandle fldHandle)
         }
 
         [Obsolete("OffsetToStringData has been deprecated. Use string.GetPinnableReference() instead.")]
-        public static int OffsetToStringData
-        {
-            [Intrinsic]
-            get => OffsetToStringData;
-        }
+        public static int OffsetToStringData => string.OFFSET_TO_STRING;
 
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
         private static extern int InternalGetHashCode(object? o);

src/mono/System.Private.CoreLib/src/System/String.Mono.cs

@@ -30,6 +30,12 @@ public static string IsInterned(string str)
         [MethodImplAttribute(MethodImplOptions.InternalCall)]
         private static extern string InternalIntern(string str);
 
+#if TARGET_64BIT
+        internal const int OFFSET_TO_STRING = 20;
+#else
+        internal const int OFFSET_TO_STRING = 12;
+#endif
+
         // TODO: Should be pointing to Buffer instead
         #region Runtime method-to-ir dependencies
 

src/mono/mono/mini/interp/transform.c

@@ -2305,16 +2305,7 @@ interp_handle_intrinsics (TransformData *td, MonoMethod *target_method, MonoClas
 			*op = MINT_INITBLK;
 		}
 	} else if (in_corlib && !strcmp (klass_name_space, "System.Runtime.CompilerServices") && !strcmp (klass_name, "RuntimeHelpers")) {
-		if (!strcmp (tm, "get_OffsetToStringData")) {
-			g_assert (csignature->param_count == 0);
-			int offset = MONO_STRUCT_OFFSET (MonoString, chars);
-			interp_add_ins (td, MINT_LDC_I4);
-			WRITE32_INS (td->last_ins, 0, &offset);
-			push_simple_type (td, STACK_TYPE_I4);
-			interp_ins_set_dreg (td->last_ins, td->sp [-1].local);
-			td->ip += 5;
-			return TRUE;
-		} else if (!strcmp (tm, "GetHashCode") || !strcmp (tm, "InternalGetHashCode")) {
+		if (!strcmp (tm, "GetHashCode") || !strcmp (tm, "InternalGetHashCode")) {
 			*op = MINT_INTRINS_GET_HASHCODE;
 		} else if (!strcmp (tm, "TryGetHashCode")) {
 			*op = MINT_INTRINS_TRY_GET_HASHCODE;

src/mono/mono/mini/intrinsics.c

@@ -935,10 +935,7 @@ mini_emit_inst_for_method (MonoCompile *cfg, MonoMethod *cmethod, MonoMethodSign
 		} else
 			return NULL;
 	} else if (cmethod->klass == runtime_helpers_class) {
-		if (strcmp (cmethod->name, "get_OffsetToStringData") == 0 && fsig->param_count == 0) {
-			EMIT_NEW_ICONST (cfg, ins, MONO_STRUCT_OFFSET (MonoString, chars));
-			return ins;
-		} else if (!strcmp (cmethod->name, "GetRawData")) {
+		if (!strcmp (cmethod->name, "GetRawData")) {
 			int dreg = alloc_preg (cfg);
 			EMIT_NEW_BIALU_IMM (cfg, ins, OP_PADD_IMM, dreg, args [0]->dreg, MONO_ABI_SIZEOF (MonoObject));
 			return ins;