Lua Generator using IR. (#6940)

* initial hack to get new Lua generator into flatc

* Starting to output enum defs for Lua

* Continue to work on table generation for Lua

* Finished basic getter access for Lua

* Added ability to get object by index

* Finished struct builder

* aliased reflection to r

* finish table builder generation

* register requiring files

* better generated header info

* Tying up loose ends

* Updated reflection to handle struct padding

* Addd type sizes to reflection

* Fixed some vector indirect issues

* Lua tests passed

* Misc cleanup

* ci fixes 1

* ci fixes 2

* renaming

* up size of type sizes

* manually ran clang-format-11 -i src/idl_parser.cpp

* fixed some windows casting

* remove stupid auto import

* more static_casting

* remove std

* update other build environments

* remove scoped enums

* replaced std::to_string with NumToString

* more win fixes

* more win fixes

* replaced old lua with new

* removed auto import

* review responses

* more style fixes

* refactor bfbs_gen_len to use code +=

* added consts

* fix lambda capture for windows

* remove unused return type

CMakeLists.txt

@@ -92,6 +92,7 @@ set(FlatBuffers_Library_SRCS
   include/flatbuffers/allocator.h
   include/flatbuffers/array.h
   include/flatbuffers/base.h
+  include/flatbuffers/bfbs_generator.h
   include/flatbuffers/buffer.h
   include/flatbuffers/buffer_ref.h
   include/flatbuffers/default_allocator.h
@@ -139,7 +140,10 @@ set(FlatBuffers_Compiler_SRCS
   src/idl_gen_swift.cpp
   src/flatc.cpp
   src/flatc_main.cpp
+  src/bfbs_gen.h
+  src/bfbs_gen_lua.h
   include/flatbuffers/code_generators.h
+  src/bfbs_gen_lua.cpp
   src/code_generators.cpp
   grpc/src/compiler/schema_interface.h
   grpc/src/compiler/cpp_generator.h