Use ConvertCase instead of Make{Upper,Lower,Snake} implementations (#7127)

* Unified name case conversion to single method

* Convert bfbs_gen to use ConvertCase

* convert rust to use ConvertCase

* Convert idl_parser to use ConvertCase

* Convert MakeScreamingCamel to ConvertCase

* Replaced MakeCamel with ConvertCase

* minor fixes

include/flatbuffers/idl.h

@@ -1057,10 +1057,6 @@ class Parser : public ParserState {
 
 // Utility functions for multiple generators:
 
-extern std::string MakeCamel(const std::string &in, bool first = true);
-
-extern std::string MakeScreamingCamel(const std::string &in);
-
 // Generate text (JSON) from a given FlatBuffer, and a given Parser
 // object that has been populated with the corresponding schema.
 // If ident_step is 0, no indentation will be generated. Additionally,

include/flatbuffers/util.h

@@ -685,6 +685,26 @@ bool ReadEnvironmentVariable(const char *var_name,
 // MSVC specific: Send all assert reports to STDOUT to prevent CI hangs.
 void SetupDefaultCRTReportMode();
 
+enum class Case {
+  kUnknown = 0,
+  // TheQuickBrownFox
+  kUpperCamel = 1,
+  // theQuickBrownFox
+  kLowerCamel = 2,
+  // the_quick_brown_fox
+  kSnake = 3,
+  // THE_QUICK_BROWN_FOX
+  kScreamingSnake = 4,
+  // THEQUICKBROWNFOX
+  kAllUpper = 5,
+  // thequickbrownfox
+  kAllLower = 6,
+};
+
+// Convert the `input` string of case `input_case` to the specified `output_case`.
+std::string ConvertCase(const std::string &input, Case output_case,
+                    Case input_case = Case::kSnake);
+
 }  // namespace flatbuffers
 
 #endif  // FLATBUFFERS_UTIL_H_