[datalog] Overload DataLogReaderThread::GetEntry to accept an entry id (#8152)

It is useful when programmatically interacting with DataLogs to be able to retrieve an record's associated metadata (entry name, type, and metadata string), but the only reference to an entry that a record contains is the id. DataLogReaderThread already builds a map of id->DataLogReaderEntry, but it was unexposed until now.

datalog/src/main/native/include/wpi/datalog/DataLogReaderThread.h

@@ -78,6 +78,15 @@ class DataLogReaderThread {
     return &it->second;
   }
 
+  const DataLogReaderEntry* GetEntry(int entry) const {
+    std::scoped_lock lock{m_mutex};
+    auto it = m_entriesById.find(entry);
+    if (it == m_entriesById.end()) {
+      return nullptr;
+    }
+    return it->second;
+  }
+
   wpi::StructDescriptorDatabase& GetStructDatabase() { return m_structDb; }
 #ifndef NO_PROTOBUF
   wpi::ProtobufMessageDatabase& GetProtobufDatabase() { return m_protoDb; }