(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}

modules/audio_processing/transient/file_utils_unittest.cc

@@ -17,7 +17,7 @@
 
 #include "rtc_base/system/file_wrapper.h"
 #include "test/gtest.h"
-#include "test/testsupport/fileutils.h"
+#include "test/testsupport/file_utils.h"
 
 namespace webrtc {
 

modules/audio_processing/transient/transient_detector_unittest.cc

@@ -18,7 +18,7 @@
 #include "rtc_base/strings/string_builder.h"
 #include "rtc_base/system/file_wrapper.h"
 #include "test/gtest.h"
-#include "test/testsupport/fileutils.h"
+#include "test/testsupport/file_utils.h"
 
 namespace webrtc {
 

modules/audio_processing/transient/transient_suppression_test.cc

@@ -21,7 +21,7 @@
 #include "modules/audio_processing/agc/agc.h"
 #include "rtc_base/flags.h"
 #include "test/gtest.h"
-#include "test/testsupport/fileutils.h"
+#include "test/testsupport/file_utils.h"
 
 WEBRTC_DEFINE_string(in_file_name, "", "PCM file that contains the signal.");
 WEBRTC_DEFINE_string(detection_file_name,

modules/audio_processing/transient/wpd_tree_unittest.cc

@@ -18,7 +18,7 @@
 #include "rtc_base/strings/string_builder.h"
 #include "rtc_base/system/file_wrapper.h"
 #include "test/gtest.h"
-#include "test/testsupport/fileutils.h"
+#include "test/testsupport/file_utils.h"
 
 namespace webrtc {