WIP: Improve performance of Wrap Map (#16761)

We've ran into performance issues when reinserting new blocks into the
assistant panel; in profiles WrapMap showed up, as we try to query wrap
boundaries over and over, which is a hidden O(n^2) - for each block, we
may potentially look at all of the Wraps. This PR alleviates this issue
by storing away previously resolved wrap range; consecutive iterations
can often reuse it.
This should help with performance of Assistant Panel with long
conversations.

Release Notes:

- Improved performance of assistant panel with large # of text.