for table views, do one query, cancel it and then run the count #3982

Right now when opening/filtering a large table, it takes very long see results. It runs a count and a query separately.

Instead, how about this:

• start the query and step to get rows, update the ui every 30ms
• once you have enough rows for a screenful:
  • if it was delivering results fast (<1s for a screenful)
    • cancel the query and run the count
    • if the user scrolls while running the count, cancel the count and do the query with the offset. Repeat.
  • otherwise:
    • keep loading the results into memory up to the limit
    • if there are less than limit results, you have the count
    • otherwise, show >$limit for the count

basically, for slow queries cache the results in memory up to some amount and perhaps even don't try to get more results?