[VFS] Rewrote STFS to use memory mapping

- Replaced old-style buffer, buffer_length with std::span
- Added STFS and SVOD specific Entry and File classes
- Other smaller improvements

src/xenia/kernel/user_module.cc

@@ -102,7 +102,8 @@ X_STATUS UserModule::LoadFromFile(const std::string_view path) {
     // Read entire file into memory.
     // Ugh.
     size_t bytes_read = 0;
-    result = file->ReadSync(buffer.data(), buffer.size(), 0, &bytes_read);
+    result = file->ReadSync(std::span<uint8_t>(buffer.data(), buffer.size()), 0,
+                            &bytes_read);
     if (XFAILED(result)) {
       return result;
     }