Try lower MSAA level if the requested value isn't available
Closes#4471 and #4631
See merge request OpenMW/openmw!297
(cherry picked from commit b3db387512340a5e9a77427c2d7d9d88c2340056)
da0aef7a Retrieve SDL OpenGL attributes after context creation
a51e63b3 Try lower MSAA levels if OpenGL context doesn't have what we requested
c4e92a0a Update CHANGELOG.md