Add underscore at the end of known common members for C# properties

This won't remove all possibilities of naming collisions, but will address the simplest ones.
The "test" is just to add all the reserved names in a proto file: if the generated code builds, it works.
Note that before this change, using any of these field names would result in a compile-time error, so this is not a breaking change.

Generated code is in the next commit.

Fixes #8810

csharp/protos/unittest_issues.proto

@@ -169,4 +169,18 @@ message OneofWithNoneName {
     string x = 1;
     string y = 2;
   }
-}
+}
+
+// Issue 8810
+message DisambiguateCommonMembers {
+  int32 equals = 1;
+  int32 to_string = 2;
+  int32 get_hash_code = 3;
+  int32 write_to = 4;
+  int32 clone = 5;
+  int32 calculate_size = 6;
+  int32 descriptor = 7;
+  int32 merge_from = 8;
+  int32 on_construction = 9;
+  int32 parser = 10;  
+}

src/google/protobuf/compiler/csharp/csharp_helpers.cc

@@ -381,13 +381,22 @@ std::string GetFieldConstantName(const FieldDescriptor* field) {
 std::string GetPropertyName(const FieldDescriptor* descriptor) {
   // TODO(jtattermusch): consider introducing csharp_property_name field option
   std::string property_name = UnderscoresToPascalCase(GetFieldName(descriptor));
-  // Avoid either our own type name or reserved names. Note that not all names
-  // are reserved - a field called to_string, write_to etc would still cause a problem.
+  // Avoid either our own type name or reserved names.
   // There are various ways of ending up with naming collisions, but we try to avoid obvious
-  // ones.
+  // ones. In particular, we avoid the names of all the members we generate or inherit.
   if (property_name == descriptor->containing_type()->name()
       || property_name == "Types"
-      || property_name == "Descriptor") {
+      || property_name == "Descriptor"
+      || property_name == "Equals"
+      || property_name == "ToString"
+      || property_name == "GetHashCode"
+      || property_name == "WriteTo"
+      || property_name == "Clone"
+      || property_name == "CalculateSize"
+      || property_name == "Descriptor"
+      || property_name == "MergeFrom"
+      || property_name == "OnConstruction"
+      || property_name == "Parser") {
     property_name += "_";
   }
   return property_name;