enhance(scatter): remove entities from the data table that are not displayed in the chart

[sophiamersmann]

fixes #2692

Problem

• In scatter plot charts, entities without data along the x- and y-axis ended up being displayed in the data table because they did have data for the size dimension (often, the size dimension is population)

Solution

This PR makes sure that only entities show up in the data table that are actually displayed in the chart:

• Entities in scatter plots that don't have data for the x- and y-dimension are removed from the table view
• Entities in scatter plots and Marimekko charts that were manually excluded by the author are also removed from the table view

Technical details

• Grapher has a new computed property, tableForDisplay
• Each chart type optionally can have a transformTableForDisplay method that produces tableForDisplay
• tableForDisplay is passed to <DataTable />

[marcelgerber]

Nicely done, this makes lots of sense and I like the tableForDisplay approach!

[github-actions]

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