mesa: add gl_coontext::ForceIntegerTexNearest

mesa: add gl_coontext::ForceIntegerTexNearest

Some applications incorrectly use GL_LINEAR* values for integers texture.
copyimage.c already implemented a tolerance for such app in prepare_target_err.

This commit adds a boolean that will treat GL_LINEAR* filters as
GL_NEAREST for integer textures.

CC: 20.1 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4647>