Add support for GetProcAddress, even without gl emulation, for Regal.  Also implement simple touch events in SDL.

Fixes up a few things in egl/glGetProcAddress and adds support for it always.
Also adds an eglGetProcAddressEMSCRIPTEN function so that it can be accessible statically even if someone overrides eglGetProcAddress.

A separate commit adds simple touch event support to SDL, by translating touches to mouse events.