Move some video codec constants to separate file.

kMaxSimulcastStreams, kMaxSpatialLayers and kMaxTemporalStreams don't
really beling on VideoBitrateAllocation.
common_types.h is going away and it feels dubious to requrie include
of the full VideoEncoder api to use them. Therefore moving them into a
seprate file/target.

Also includes some remaining cleanup of includes.

Bug: webrtc:9271
Change-Id: I7ded3d97a9a835ac756159700774445a2b93a697
Reviewed-on: https://webrtc-review.googlesource.com/c/117305
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26299}

modules/include/module_common_types.h

@@ -13,6 +13,7 @@
 
 #include <stddef.h>
 #include <stdint.h>
+#include <vector>
 
 #include "api/rtp_headers.h"
 #include "common_types.h"  // NOLINT(build/include)