Fix possible Windows GPU multiple window crash

[andydotxyz]

This was a real pain!
On some GPUs the new shaders would crash when in the background.
It appears to be like the discovered webGL issue before but worse.
This fix addresses both at the same time.

Tested in Windows Intel, webGL and also GLES code paths.

Fixes #4000

Checklist:

• Tests included. <- see the issue for steps (you'll need the right GPU)
• Lint and formatter run with no errors.
• Tests all pass.

[coveralls]

coverage: 66.189% (-0.02%) from 66.204% when pulling 8ddd2ef on andydotxyz:fix/4000 into 19e0c73 on fyne-io:develop.

[Goltanju]

👍 Works great here. Verified develop failed, then that fix/4000 passed. nVidia GeForce RTX 2080 Ti on Windows 11.

That looks like it was "fun". Thankyou!

[Jacalz]

While I haven't been able to reproduce the issue myself, the code does look good and works fine on my computer. Well done!

Just had one not inline about a file that probably shouldn't be deleted. Consider it approved after that :)

[Bluebugs]

I have some swear word I want to use about GL driver. Good catch. Thanks for tracking this down.