[Lens] previous bucket in formula

[ghudgins]

Describe the feature:
Expose functions that allow formula to construct with previous bucket of a date histogram to build more advanced calculations than the differences quick function. Would also need to consider gap fill policy #115761

Describe a specific use case for the feature:
When I want to write a moving percentage difference in formula
And I am visualizing with a date histogram
I need to pull a value from the previous bucket on the visualization
So I can do things like count() / previous_bucket(count()) -1 to get at moving percentage

[elasticmachine]

Pinging @elastic/kibana-vis-editors (Team:VisEditors)

[ghudgins]

Related to: #62381
This issue was descoped from: #104259

[flash1293]

To allow the "serial diff" functionality, it should be nth previous bucket (can be done by an optional parameter defaulting to one: previous_bucket(count(), delta=5))

[markov00]

Closing this because it's not planned to be resolved in the foreseeable future. It will be tracked in our Icebox and will be re-opened if our priorities change. Feel free to re-open if you think it should be melted sooner.