Enhancement: Indicate Map Block Limitations in UI

### Impacted plugin

Jetpack

### What

Indicate limitations of map block and how many items can be added before they are rendered as a list.

### How

On WPCOM sites, the Jetpack Map Block hits a limit once you place more than 37 items in close proximity to each other. At that point, the map renders as a list rather than a map.

This limitation did not affect self-hosted Jetpack.

## Screenshot

Reported on:
7417-gh-Automattic/jpop-issues

Start by locating the Jetpack Map Block UI and checking how WPCOM sites switch from a map to a list when nearby items exceed the limit. Confirm whether the 37-item limitation is exposed in the relevant UI context. Done means the limitation and item threshold are clearly indicated for affected sites without changing self-hosted Jetpack behavior.

Written by the indexing model from the issue text.