Additionally create "_next" permutations for all of the test binaries
on Fuchsia, in order to test both code-paths.
Using the #define follow-up CLs can also create a flutter_runner_next
binary that does not contain any legacy integration code.
BUG: 53847
Flow is a simple compositor based on Skia that the Flutter engine uses to cache
recoded paint commands and pixels generated from those recordings. Flow runs on
the raster thread and uploads information to Skia.