(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}

api/rtp_parameters.h

@@ -8,8 +8,8 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef API_RTPPARAMETERS_H_
-#define API_RTPPARAMETERS_H_
+#ifndef API_RTP_PARAMETERS_H_
+#define API_RTP_PARAMETERS_H_
 
 #include <stdint.h>
 #include <string>
@@ -17,7 +17,7 @@
 #include <vector>
 
 #include "absl/types/optional.h"
-#include "api/mediatypes.h"
+#include "api/media_types.h"
 #include "rtc_base/system/rtc_export.h"
 
 namespace webrtc {
@@ -673,4 +673,4 @@ struct RTC_EXPORT RtpParameters {
 
 }  // namespace webrtc
 
-#endif  // API_RTPPARAMETERS_H_
+#endif  // API_RTP_PARAMETERS_H_