(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}

pc/sdp_utils.h

@@ -8,15 +8,15 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#ifndef PC_SDPUTILS_H_
-#define PC_SDPUTILS_H_
+#ifndef PC_SDP_UTILS_H_
+#define PC_SDP_UTILS_H_
 
 #include <functional>
 #include <memory>
 #include <string>
 
 #include "api/jsep.h"
-#include "pc/sessiondescription.h"
+#include "pc/session_description.h"
 
 namespace webrtc {
 
@@ -57,4 +57,4 @@ void SdpContentsForEach(SdpContentMutator fn,
 
 }  // namespace webrtc
 
-#endif  // PC_SDPUTILS_H_
+#endif  // PC_SDP_UTILS_H_