plugin: Add GL uploader

Add "clappergluploader" module which uses "glupload" and "glcolorconvert" internally,
allowing either uploading RAW system memory into GPU with GL colorspace conversion or
importing DMABufs into GL memory and making a GdkTexture out of them at one go.

lib/gst/plugin/importers/meson.build

@@ -14,6 +14,7 @@ endif
 
 plugin_needs_gl_base = (
   not get_option('glimporter').disabled()
+  or not get_option('gluploader').disabled()
 )
 
 gst_plugin_gl_deps = [gstgl_dep, gstglproto_dep]
@@ -50,6 +51,8 @@ foreach dep : gst_clapper_gl_base_importer_deps
   if not dep.found() or not have_gtk_gl_windowing
     if get_option('glimporter').enabled()
       error('GL importer was enabled, but required dependencies were not found')
+    elif get_option('gluploader').enabled()
+      error('GL uploader was enabled, but required dependencies were not found')
     endif
     plugin_needs_gl_base = false
   endif
@@ -81,3 +84,15 @@ if not get_option('glimporter').disabled() and gst_clapper_gl_base_importer_dep.
     install_dir: gst_clapper_importers_libdir,
   )
 endif
+
+if not get_option('gluploader').disabled() and gst_clapper_gl_base_importer_dep.found()
+  library(
+    'gstclappergluploader',
+    'gstclappergluploader.c',
+    dependencies: gst_clapper_gl_base_importer_dep,
+    include_directories: configinc,
+    c_args: gst_clapper_plugin_args,
+    install: true,
+    install_dir: gst_clapper_importers_libdir,
+  )
+endif