[wpilibj] DataLogManager: Fix behavior when low on space (#6486)

Uses getUsableSpace in Java, matching how C++ determines available space (C++ calls it available, but they mean the same thing.) This fixes a bug where logs wouldn't get deleted due to incorrect available space detection.

The DataLog thread now also checks if the state was marked as stopped after a call to StartLogFile.

wpiutil/src/main/native/cpp/DataLog.cpp

@@ -463,6 +463,9 @@ void DataLog::WriterThreadMain(std::string_view dir) {
       lock.unlock();
       StartLogFile(state);
       lock.lock();
+      if (m_state == kStopped) {
+        continue;
+      }
       if (state.f != fs::kInvalidFile) {
         // Emit start and schema data records
         for (auto&& entryInfo : m_entries) {