Adopt absl::string_view in testsupport/file_utils*

Bug: webrtc:13579
Change-Id: I5b710cfd218c44be01a7a42c2b281739081881e6
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/256280
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Ali Tofigh <alito@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36332}

test/testsupport/ios_file_utils.h

@@ -13,12 +13,15 @@
 
 #include <string>
 
+#include "absl/strings/string_view.h"
+
 namespace webrtc {
 namespace test {
 
 std::string IOSOutputPath();
 std::string IOSRootPath();
-std::string IOSResourcePath(std::string name, std::string extension);
+std::string IOSResourcePath(absl::string_view name,
+                            absl::string_view extension);
 
 }  // namespace test
 }  // namespace webrtc