[Canvas] Filtered elements do not change if filter expression is changed until the new filter value is selected

[poffdeluxe]

Kibana version:
Checked on 7.9.1 and master

Describe the bug:
If you have a dropdown filter on a workpad and then you modify the filter's expression (for example to retrieve a different field in a query or to change the field which is being filtered), elements that use the filters function in their expression will not update until a new option is selected from the filter dropdown.

Steps to reproduce:

1. Add the default filter dropdown to a workpad
2. Add a debug filter element to the workpad
3. Change the filter expression so that it displays and filters the state column
4. The debug filter element still shows info about the old filter

Expected behavior:
The elements that rely on the filter should be updated when the filter updates

Screenshots (if relevant):

[elasticmachine]

Pinging @elastic/kibana-canvas (Team:Canvas)

[ThomThomson]

Closing this as we are not prioritizing Canvas editing experience enhancements for the time being. We can reopen this if it becomes a priority again.