uidriver/mobile: Bug fix: Freeze on Pixel 4
uidriver/mobile: Bug fix: Freeze on Pixel 4

An Ebiten application often freezes on Pixel 4. Apparently adding
loggings or runtime.Gosched hides the issue, though this doesn't fix
the root cause. The root cause might be in gomobile itself, but it
seeems really hard to make a minimum case.

As a tentative fix, add runtime.Gosched to avoid freezing.

Fixes #1322

hajimehoshi/ebiten,hajimehoshi/ebiten