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Did not test on platforms other than my phone, but I can't imagine it
causing problems. AFAIK if highp isn't supported then `precision highp
float;` needs to still not cause the program to fail to link/compile or
anything; it should just silently use some other precision.
* Fixes https://github.com/emilk/egui/issues/4268 for me but I only
tested it on a native Android app and I don't know whether backends
other than glow are affected.
* [x] I have followed the instructions in the PR template (but the
change is trivial so I'm just doing it from the master branch)
Before:

After:
