Describe the bug
Self time is incorrectly reported when multiple threads are merged in the view. The Self time values are not merged, only one is shown

To Reproduce

1. Open a snapshot with multiple threads where Self time takes up a noticeable amount of time (eg: here)
2. Merge those threads
3. Check reported Self time

Expected behavior
Self time to be merged between the selected threads as all other methods are

Screenshots

Desktop (please complete the following information):

• Debian 10
• JDK version - any
• Version 2.0.6