Enforce the maximum texture size limit both for textures and renderbuffers, showing warnings and adjusting the size automatically. On the low end ES 2.0 devices we can easily hit a maximum size of 2048x2048. For example a Raspberry Pi running in full HD with the Controls 2 Material style breaks right away as it tries to create slightly wider than 2048 texture for its ShaderEffect. Instead of breaking with an obscure framebuffer incomplete warning at best, show something more informative and adjust the sizes so that something shows up on the screen still. (naturally applications not taking the maximum sizes returned from QRhi into account are technically incorrect and may well end up with incorrect rendering, but we should still try handling this as gracefully as possible) Change-Id: Ib75eb893ab4774e1a3c49ed2d14c6bf9be8c807a Reviewed-by: Lars Knoll <lars.knoll@qt.io>