Fix swizzling when rendering QPainter on QOpenGLWidget with Angle

OpenGLES specification does not support GL_TEXTURE_SWIZZLE_RGBA,
it supports only per-channel calls. And since Qt supports QpenGLES,
it should use the latter approach only.

See the upstream patch review:
https://codereview.qt-project.org/#/c/258193/

BUG:406196