Bump SDL to build with 10.7 SDK.

This also bumps the minimum requirement for building SDL to 10.7, and
removes some checking we no longer need.

CR: saml
Make sure our window has mouse focus before processing raw input events.
This happens rarely, but not reproducibly, where we get raw input events for the window even though it doesn't have focus.
Switch back to apartment threaded COM initialization, which was the previous default.
We do succeed now if the application previously initialized COM in multi-threaded mode.