Inline evaluation result dissapears after a second

[glebovmaksim]

The root of the problem is the decoration cleaning event. It fires not only when the content of the document changes, but also after saving the file. So, if my auto-save setting is on and I press alt+enter right after some typing, the following happens:

1. The evaluation result appears.
2. Auto save is performed.
3. onDidChangeTextDocument event cleans the decoration.

The suggested fix is to clean the decoration only if the event contains real changes. PR is coming.