(4) Rename files to snake_case: update BUILD.gn, include paths, header guards, and DEPS entries

Mechanically generated by running this command:

tools_webrtc/do-renames.sh update all-renames.txt && git cl format

Then manually updating:

tools_webrtc/sanitizers/tsan_suppressions_webrtc.cc

Bug: webrtc:10159
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I54824cd91dada8fc3ee3d098f971bc319d477833
Reviewed-on: https://webrtc-review.googlesource.com/c/115653
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26226}
diff --git a/pc/rtcp_mux_filter.cc b/pc/rtcp_mux_filter.cc
index dceaf46..a8cf717 100644
--- a/pc/rtcp_mux_filter.cc
+++ b/pc/rtcp_mux_filter.cc
@@ -8,7 +8,7 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#include "pc/rtcpmuxfilter.h"
+#include "pc/rtcp_mux_filter.h"
 
 #include "rtc_base/logging.h"