Make QSGTexture, QSGPlainTexture, and related OpenGL-clean

Split from QTBUG-84623.

virtual int textureId() const = 0; // ### Qt 6: remove
virtual void bind() = 0; // ### Qt 6: remove
void updateBindOptions(bool force = false); // ### Qt 6: remove

plus some helper function in qsgtexture.cpp can be removed as well.

Same goes for QSGPlainTexture, the overrides of these functions are to be removed.

Remove the OpenGL texture atlas.

Then it has effects in various places (painter node, etc.) clean those up.