This is for Fuchsia where we would like it to be located at //third_party/flutter.

* 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

This repository contains FTL now in the Fuchsia build.

Update targets only included in host_debug_unopt.

This reverts commit f5d0004e.

* add paths_win.cc to FML

* update licenses

* 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.