Support density views in theia

[tahini]

trafficstars

• [ ] In Trace Compass, density data should be provided by data providers. It can maybe use the existing XY data provider, but using a different scale
• [ ] The density viewers in Trace Compass should use the data provider
• [ ] Theia should support this view type too. The different X axis may be tricky.
• [ ] Support many density series

[tahini]

[MatthewKhouzam]

Here is an option to overlay it with the XY Scatter chart.

[MatthewKhouzam]

By doing this, we minimize the round trips to the server too.