* Fix remaining ftl->fxl conversions
The previous scripting pass at this did not account for objective c file endings
* Update tonic DEPS reference to the post-fxl version
* Partially port FML to Windows.
* Adds a message loop impl for Windows
* Ports `thread.cc` to Windows
All FML unittests are now passing on Windows.
FML as a whole does not compile on windows yet because `mapping.cc` imports `sys/mman.h`, which is not available on Windows and the replacement API for memory-mapped files is very different on Windows, see https://msdn.microsoft.com/en-us/library/windows/desktop/aa366556%28v=vs.85%29.aspx.
* update licenses
* review comments
* Maintain FlutterTextInputView text in NSMutableString
We were converting from/to NSString at the interface of
FlutterTextInputView; instead use NSMutableString to maintain the
internal buffer.
Eliminates nsstring_utils.{h,mm} which no longer has any users.
