[C++] Check for case insensitive keywords (#8420)

* chore(idl): Check for case insensitive keywords

Most languages are not affected by this change. In PHP, some names such
as Bool cannot be used because it is a reserved keyword for to the bool
data type. The field `keywords_casing` in the configs enables checking
all characters in lowercase against every keyword. This should be safe
as flatbuffers does not allow non-ASCII characters in its grammar.

* chore: Fix formatting to follow google's coding style for enums

* chore: Extract convert case to lower when CaseInsensitive

---------

Co-authored-by: Justin Davis <jtdavis777@gmail.com>
Co-authored-by: Derek Bailey <derekbailey@google.com>

include/codegen/python.h

@@ -26,6 +26,7 @@ static const Namer::Config kConfig = {
     /*object_suffix=*/"T",
     /*keyword_prefix=*/"",
     /*keyword_suffix=*/"_",
+    /*keywords_casing=*/Namer::Config::KeywordsCasing::CaseSensitive,
     /*filenames=*/Case::kKeep,
     /*directories=*/Case::kKeep,
     /*output_path=*/"",
@@ -49,6 +50,7 @@ static const Namer::Config kStubConfig = {
     /*object_suffix=*/"T",
     /*keyword_prefix=*/"",
     /*keyword_suffix=*/"_",
+    /*keywords_casing=*/Namer::Config::KeywordsCasing::CaseSensitive,
     /*filenames=*/Case::kKeep,
     /*directories=*/Case::kKeep,
     /*output_path=*/"",