Add Code Generator for idl_gen_fbs to parse .proto files (#7832)

* Add code generator for proto files

* Update

* Add --proto to script

* Remove cmt

* Move proto parsing logic into else block to share same set up logic for code_generator

* Remove IsValidCodeGenerator

src/flatc_main.cpp

@@ -27,6 +27,7 @@
 #include "idl_gen_cpp.h"
 #include "idl_gen_csharp.h"
 #include "idl_gen_dart.h"
+#include "idl_gen_fbs.h"
 #include "idl_gen_go.h"
 #include "idl_gen_java.h"
 #include "idl_gen_json_schema.h"
@@ -100,6 +101,11 @@ int main(int argc, const char *argv[]) {
                                 "Generate Dart classes for tables/structs" },
       flatbuffers::NewDartCodeGenerator());
 
+  flatc.RegisterCodeGenerator(
+      flatbuffers::FlatCOption{ "", "proto", "",
+                                "Input is a .proto, translate to .fbs" },
+      flatbuffers::NewFBSCodeGenerator());
+
   flatc.RegisterCodeGenerator(
       flatbuffers::FlatCOption{ "g", "go", "",
                                 "Generate Go files for tables/structs" },