Add experimental wayland support. Refs #853

* This is only lightly tested and may break heavily. It is disabled by default
 and must be explicitly enabled.
* In particular this is only known to work for Wayland use at capture time.
 Wayland on replay is still unsupported. Known issues include: EGL pbuffer
 surfaces are not implemented on Wayland, Wayland cannot get window dimensions,
 and there are hangs/failures with GL and vulkan presentation with Wayland.

renderdoccmd/renderdoccmd_linux.cpp

@@ -537,6 +537,11 @@ int main(int argc, char *argv[])
     count++;
 #endif
 
+#if defined(RENDERDOC_WINDOWING_WAYLAND)
+    support += "Wayland (CAPTURE ONLY), ";
+    count++;
+#endif
+
 #if defined(RENDERDOC_SUPPORT_VULKAN)
     support += "Vulkan KHR_display, ";
     count++;