Allow requesting core OpenGL profile and explicit OpenGL version.

Add WX_GL_CORE_PROFILE and WX_GL_{MAJOR,MINOR}_VERSION attributes which can be
used to use modern OpenGL with wxGLCanvas.

Closes #16402.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@77018 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775