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

tests/TableA.lua

@@ -0,0 +1,51 @@
+--[[ TableA
+
+  Automatically generated by the FlatBuffers compiler, do not modify.
+  Or modify. I'm a message, not a cop.
+
+  flatc version: 2.0.0
+
+  Declared by  : //include_test/include_test1.fbs
+  Rooting type : MyGame.Example.Monster (//monster_test.fbs)
+
+--]]
+
+local __MyGame_OtherNameSpace_TableB = require('MyGame.OtherNameSpace.TableB')
+local flatbuffers = require('flatbuffers')
+
+local TableA = {}
+local mt = {}
+
+function TableA.New()
+  local o = {}
+  setmetatable(o, {__index = mt})
+  return o
+end
+
+function mt:Init(buf, pos)
+  self.view = flatbuffers.view.New(buf, pos)
+end
+
+function mt:B()
+  local o = self.view:Offset(4)
+  if o ~= 0 then
+    local x = self.view:Indirect(self.view.pos + o)
+    local obj = __MyGame_OtherNameSpace_TableB.New()
+    obj:Init(self.view.bytes, x)
+    return obj
+  end
+end
+
+function TableA.Start(builder)
+  builder:StartObject(1)
+end
+
+function TableA.AddB(builder, b)
+  builder:PrependStructSlot(0, b, 0)
+end
+
+function TableA.End(builder)
+  return builder:EndObject()
+end
+
+return TableA