Add support for Bambu Lab X1 series live video stream on Linux.

wxWidgets on Linux uses GStreamer as its back-end for wxMediaCtrl, which
doesn't have a bambu: URI handler.  On Windows, this is handled by a Windows
Media subsystem plugin, and on Mac, this is handled with a BambuPlayer
class.  Luckily, the libBambuSource.so binary that is distributed with the
network plugin package already contains support for receiving h.264 data
from the network, and the API is the same as is used by the tiny
bambusource.exe binary on Windows; we glue this into a GStreamer source
plugin that registers a URI handler for bambu:.

To make this work, we make a few additional changes elsewhere.  GStreamer
seems to have trouble rendering an Xv overlay onto a 32bpp X visual, but
Bambu Slicer seems to request a 32bpp visual for some background
transparency in the Notebook; it doesn't seem to use it in an interesting
way on Linux, though, so we remove that request for transparency to allow
Bambu Studio to render to a 24bpp visual.  The media controller
infrastructure also makes a few assumptions about when sizing information
can be queried from a wxMediaCtrl backend that do not hold true on Linux; we
either fix those assumptions, or fake them out, as needed.  We also make a
few changes needed to successfully compile C.

This has only been tested with the GStreamer backend for wxWidgets --
notably, not the GStreamer-play backend (these are, astonishingly, two
different things!).  If you find that this seems not to work, consider
*un*installing the libgstreamer-plugins-bad1.0-dev package and then
rebuilding wxWidgets.

src/slic3r/GUI/MediaPlayCtrl.cpp

@@ -541,7 +541,11 @@ bool MediaPlayCtrl::get_stream_url(std::string *url)
 
 void wxMediaCtrl2::DoSetSize(int x, int y, int width, int height, int sizeFlags)
 {
+#ifdef __WXMAC__
     wxWindow::DoSetSize(x, y, width, height, sizeFlags);
+#else
+    wxMediaCtrl::DoSetSize(x, y, width, height, sizeFlags);
+#endif
     if (sizeFlags & wxSIZE_USE_EXISTING) return;
     wxSize size = GetVideoSize();
     if (size.GetWidth() <= 0)