Resize state machine: A fix and a question (#2929)

* Store EGFX state before entering resize state machine

At present the EGFX state is destroyed by states WMRZ_EGFX_DELETE_SURFACE
through WRMZ_EGFX_DELETE. This means that at WMRZ_EGFX_INITIALIZE we
cannot distinguish between EGFX not being ever used, and EGFX
having been torn down. Consequently, when running non-GFX, we don't
correctly recover the session.

* Allow multiple reasons for suppress_output

Replaces the single boolean for suppress_output with
a bitmask, to allow output to be suppressed for
more than one reason

* Disable output during resize

* Add states to dynamic resize

Adds states to the dynamic resize state machine so we wait for a
Deactivation-Reactivation sequence to finish before sending pointer
updates, etc.

* suppress module output during the dynamic resize

* Add support for dynamic resize to VNC backend

xrdp_mm needs to be informed when a resize has been performed so that
the resize stte machine can be updsate.

vnc/vnc.c

@@ -1249,6 +1249,12 @@ lib_framebuffer_waiting_for_resize_confirm(struct vnc *v)
             {
                 LOG(LOG_LEVEL_DEBUG, "VNC server successfully resized");
                 log_screen_layout(LOG_LEVEL_INFO, "NewLayout", &layout);
+                // If this resize was requested by the client mid-session
+                // (dynamic resize), we need to tell xrdp_mm that
+                // it's OK to continue with the resize state machine.
+                // We do this by sending a reset with bpp == 0
+                error = v->server_reset(v, v->server_width,
+                                        v->server_height, 0);
             }
             else
             {