linux-capture: Add getters for portal's D-Bus connection and proxy

It'll be used by the next commit to reuse these objects instead of creating
one per capture.

plugins/linux-capture/portal.c

@@ -72,3 +72,15 @@ uint32_t portal_get_available_capture_types(void)
 
 	return available_source_types;
 }
+
+GDBusConnection *portal_get_dbus_connection(void)
+{
+	ensure_proxy();
+	return connection;
+}
+
+GDBusProxy *portal_get_dbus_proxy(void)
+{
+	ensure_proxy();
+	return proxy;
+}

plugins/linux-capture/portal.h

@@ -21,5 +21,9 @@
 #pragma once
 
 #include <stdint.h>
+#include <gio/gio.h>
 
 uint32_t portal_get_available_capture_types(void);
+
+GDBusConnection *portal_get_dbus_connection(void);
+GDBusProxy *portal_get_dbus_proxy(void);