[osg-users] minor change: move assumeSizedInternallFormat from Texture to Image

[Robert Osfield]

Hi Julien et. al,

I have so far just focused on the 3.6 branch as this has quite well
constrained use of glTexStorage, so not so many code paths to look at.
To help clean up the sized internal format code up I have created a
GLenum Texture::selectSizedInternalFormat(const osg::Image* image)
const method in place of the original code, functionality it's very
similar, the important thing about it is that is pulls all the logical
for computing he sized internal format into a single method and cleans
up the code that requires it i.e. the glTexStorage code.

The commit to the 3.6 branch is:

    https://github.com/openscenegraph/OpenSceneGraph/commit/58a51cbc41e0ad678fb6b818c460c00098f9b727

I've now cherry picked this and am about to test master, then I'll
start looking more widely at the glTexStorage usage in master and see
if there opportunities to use this new helper method and if so will
this require further refinement of the selectSizedInternalFormat(..)
method.

Robert.