Legend needs to indicate that data set cannot fit inside

Currently, the legend (tooltip) displays information on hover. Usually, all of the data associated with a hover point is displayed. However, there are extreme cases where a hover point can be associated with thousands of data points or more. While there is no practical way to view this data, it would be helpful to get some sort of indication that the hover point has more data than can be displayed.

This is tangentially related to idpe issue 9107 - Hover points: RangeError: Maximum call stack size exceeded. That issue involves performance, due to the resources being exceeded. Solving it would still leave the issue of how to notify the user that there is too much information and not everything can be displayed.

**Suggestion**:
A message at the bottom of the legend that says, "_Additional {number} of points not shown_"

**Additional considerations**:
Color scaling should work correctly when there are large amounts of data points, but only a small subset is shown. In other words, scale the colors to the number of rendered rows rather than to the entire data set.

The issue concerns the legend tooltip, hover points with more data than can be displayed, and color scaling for large data sets. Start by locating the legend and hover-point rendering entry points, then verify that the tooltip reports omitted points and that color scaling remains correct when only a subset is rendered.

Written by the indexing model from the issue text.