Make Utf8CStr a first class citizen in C++ codebase

Utf8CStr is in many cases a better string view class than
std::string_view, because it provides "view" access to a string buffer
that is guaranteed to be null terminated. It also has the additional
benefit of being UTF-8 verified and can seemlessly cross FFI boundaries.

We would want to start use more Utf8CStr in our existing C++ codebase.

native/src/sepolicy/lib.rs

@@ -30,7 +30,6 @@ pub mod ffi {
         include!("policy.hpp");
         include!("../base/include/base.hpp");
 
-        #[namespace = "rust"]
         #[cxx_name = "Utf8CStr"]
         type Utf8CStrRef<'a> = base::ffi::Utf8CStrRef<'a>;
 

native/src/sepolicy/policydb.cpp

@@ -97,7 +97,7 @@ SePolicy SePolicy::from_data(rust::Slice<const uint8_t> data) noexcept {
     return {std::make_unique<sepol_impl>(db)};
 }
 
-SePolicy SePolicy::from_file(::rust::Utf8CStr file) noexcept {
+SePolicy SePolicy::from_file(::Utf8CStr file) noexcept {
     LOGD("Load policy from: %.*s\n", static_cast<int>(file.size()), file.data());
 
     policy_file_t pf;
@@ -235,7 +235,7 @@ static int vec_write(void *v, const char *buf, int len) {
     return len;
 }
 
-bool SePolicy::to_file(::rust::Utf8CStr file) const noexcept {
+bool SePolicy::to_file(::Utf8CStr file) const noexcept {
     // No partial writes are allowed to /sys/fs/selinux/load, thus the reason why we
     // first dump everything into memory, then directly call write system call
     vector<char> out;