cameraservice: Migrate all internal String8/String16s to std::string

String8 and String16 are deprecated classes. It is recommended to use
std::string or std::u16string wherever possible. String16 is the native
string class for aidl, but Strings marked @utf8InCpp can use std::string
directly.

This patch standardizes libcameraservice's use of strings to
std::string, which is capable of storing utf-8 strings. This makes the
code more readable and potentially reduces the number of string copies
to a minimum.

A new set of string utils is added to frameworks/av/camera to aid this
migration.

Change-Id: I59330ac03c8a52b6c21a2388bba0c143e68af4cf
Bug: 265487852
Test: Presubmit, ran CtsCameraTestCases on Cuttlefish, adb shell dumpsys media camera and observed output
diff --git a/services/camera/libcameraservice/tests/CameraProviderManagerTest.cpp b/services/camera/libcameraservice/tests/CameraProviderManagerTest.cpp
index 1a6b2e0..c0cd1a9 100644
--- a/services/camera/libcameraservice/tests/CameraProviderManagerTest.cpp
+++ b/services/camera/libcameraservice/tests/CameraProviderManagerTest.cpp
@@ -302,15 +302,15 @@
 
     ~TestStatusListener() {}
 
-    void onDeviceStatusChanged(const String8 &,
+    void onDeviceStatusChanged(const std::string &,
             CameraDeviceStatus) override {}
-    void onDeviceStatusChanged(const String8 &, const String8 &,
+    void onDeviceStatusChanged(const std::string &, const std::string &,
             CameraDeviceStatus) override {
         mPhysicalCameraStatusChangeCount++;
     }
-    void onTorchStatusChanged(const String8 &,
+    void onTorchStatusChanged(const std::string &,
             TorchModeStatus) override {}
-    void onTorchStatusChanged(const String8 &,
+    void onTorchStatusChanged(const std::string &,
             TorchModeStatus, SystemCameraKind) override {}
     void onNewProviderRegistered() override {}
 };