Scatter plots with multiple values per entry

The scatter plot widget is too limited at the moment: it can only be used to display scalar values from non-repeated structures.

To improve this, the following should be done:

• Extend the widget pydantic model to include
  • Instead of providing a string for x, y, and color, we should use more complex configuration objects that can include units, labels etc.
  • Document the possibility of using JMESPath syntax on quantity
  • Add root_validator that ensures backward compatibility with old models.
• Create a new function utility function parseJMESPath for parsing JMESPath syntax
• Create tests for parseJMESPath:
  • Raise JMESPath errors correctly
  • Handle functions
  • Handle selectors
  • Handle quantity names with schema + dtype
• Create new input component InputJMESPath for JMESPath queries
• Create tests for InputJMESPath:
  • Raise JMESPath errors correctly
  • Only allow values from current SearchContext
• Create tests for WidgetScatterPlot:
  • Test that using quantity names that target scalar values works as normal
  • Test that custom axis labels are shown correctly
  • Test that custom units are handled correctly.
  • Test that using (subset) of JMESPath syntax works:
    • selection: results.material.topology[0].cell.a
    • functions: max(results.material.topology[*].cell.a)
• Create tests for WidgetScatterPlotEdit:
  • Test that using invalid JMESPath syntax gives a warning
  • Test that targeting unavailable quantities gives warning
  • Test that invalid units gives warning
  • Test that incompatible units gives warning
  • Test that missing required values units gives warning
  • Test that targeting repeatable data with no JMESPath syntax gives a warning.