[gRPC] Update the code generator for Python to produce typed handlers (#8326)

* Move `namer.h` and `idl_namer.h` to `include/codegen` so they can be reused from `grpc` dirqectory.

* [gRPC] Update the Python generator to produce typed handlers and Python stubs if requested.

* [gRPC] Document the newly added compiler flags.

src/idl_gen_python.cpp

@@ -29,12 +29,12 @@
 #include <utility>
 #include <vector>
 
+#include "codegen/idl_namer.h"
 #include "codegen/python.h"
 #include "flatbuffers/code_generators.h"
 #include "flatbuffers/flatbuffers.h"
 #include "flatbuffers/idl.h"
 #include "flatbuffers/util.h"
-#include "idl_namer.h"
 
 namespace flatbuffers {
 namespace python {
@@ -44,52 +44,6 @@ namespace {
 typedef std::pair<std::string, std::string> ImportMapEntry;
 typedef std::set<ImportMapEntry> ImportMap;
 
-static Namer::Config PythonDefaultConfig() {
-  return { /*types=*/Case::kKeep,
-           /*constants=*/Case::kScreamingSnake,
-           /*methods=*/Case::kUpperCamel,
-           /*functions=*/Case::kUpperCamel,
-           /*fields=*/Case::kLowerCamel,
-           /*variable=*/Case::kLowerCamel,
-           /*variants=*/Case::kKeep,
-           /*enum_variant_seperator=*/".",
-           /*escape_keywords=*/Namer::Config::Escape::AfterConvertingCase,
-           /*namespaces=*/Case::kKeep,  // Packages in python.
-           /*namespace_seperator=*/".",
-           /*object_prefix=*/"",
-           /*object_suffix=*/"T",
-           /*keyword_prefix=*/"",
-           /*keyword_suffix=*/"_",
-           /*filenames=*/Case::kKeep,
-           /*directories=*/Case::kKeep,
-           /*output_path=*/"",
-           /*filename_suffix=*/"",
-           /*filename_extension=*/".py" };
-}
-
-static Namer::Config kStubConfig = {
-    /*types=*/Case::kKeep,
-    /*constants=*/Case::kScreamingSnake,
-    /*methods=*/Case::kUpperCamel,
-    /*functions=*/Case::kUpperCamel,
-    /*fields=*/Case::kLowerCamel,
-    /*variables=*/Case::kLowerCamel,
-    /*variants=*/Case::kKeep,
-    /*enum_variant_seperator=*/".",
-    /*escape_keywords=*/Namer::Config::Escape::AfterConvertingCase,
-    /*namespaces=*/Case::kKeep,  // Packages in python.
-    /*namespace_seperator=*/".",
-    /*object_prefix=*/"",
-    /*object_suffix=*/"T",
-    /*keyword_prefix=*/"",
-    /*keyword_suffix=*/"_",
-    /*filenames=*/Case::kKeep,
-    /*directories=*/Case::kKeep,
-    /*output_path=*/"",
-    /*filename_suffix=*/"",
-    /*filename_extension=*/".pyi",
-};
-
 // Hardcode spaces per indentation.
 static const CommentConfig def_comment = { nullptr, "#", nullptr };
 static const std::string Indent = "    ";
@@ -662,7 +616,7 @@ class PythonGenerator : public BaseGenerator {
       : BaseGenerator(parser, path, file_name, "" /* not used */,
                       "" /* not used */, "py"),
         float_const_gen_("float('nan')", "float('inf')", "float('-inf')"),
-        namer_(WithFlagOptions(PythonDefaultConfig(), parser.opts, path),
+        namer_(WithFlagOptions(kConfig, parser.opts, path),
                Keywords(version)) {}
 
   // Most field accessors need to retrieve and test the field offset first,