Make StringPiece to be std::string_view alias

Bug: 237583012
Test: build + boot + UTs

Change-Id: I849831f4466d3b9c7ec842b75256e7fcba77a0c0
diff --git a/cmds/idmap2/libidmap2/PolicyUtils.cpp b/cmds/idmap2/libidmap2/PolicyUtils.cpp
index 4e3f54d2..76c70ca 100644
--- a/cmds/idmap2/libidmap2/PolicyUtils.cpp
+++ b/cmds/idmap2/libidmap2/PolicyUtils.cpp
@@ -53,7 +53,7 @@
 
   for (const auto& policy : kPolicyStringToFlag) {
     if ((bitmask & policy.second) != 0) {
-      policies.emplace_back(policy.first.to_string());
+      policies.emplace_back(policy.first);
     }
   }