wsegl: also commit when requesting another frame callback for swap interval
wsegl: fix possible callback leak
wsegl: fix leak when releasing buffers
wsegl: do not use EGL stack global lock

By default the EGL stack prevents concurrent calls to the WSEGL
implementation, preventing good performance when using multiple contexts
in different threads. Handle locking ourselves to fix that.
wsegl: increase window max number of buffers to 3

This avoids a deadlock when the front buffer is used as a scanout
buffer.