🎉 (grapher) round to significant figures / TAS-537

sophiamersmann commented 3 months ago

Adds support for rounding to significant numbers, resolves https://github.com/owid/owid-grapher/issues/1851

Summary

Adds variable.display.roundingMode and variable.display.numSignificantFigures
- The roundingMode is one of decimalPlaces or significantFigures (with decimalPlaces being the default)
- If the roundingMode is decimalPlaces, we look at numDecimalPlaces; if the roundingMode is significantFigures, we look at numSignificantFigures
Rounding to significant figures relies on d3's r mode ("decimal notation, rounded to significant digits"); when rounding to sig figs, trailing zeroes are always shown
In essence, values rounded to sig figs appear everywhere expect for the table, where we use fixed-point notation

Sig fig rounded values appear in all tooltips
- If they do, the tooltip displays a note that says "Values are rounded to X significant figures" or "Values are rounded to X or Y significant figures" (if the tooltip displays values that are rounded to different numbers of sig figs)
Sig fig rounded values appear in the chart area; this includes:
- Discrete bar charts
- Stacked discrete bar charts
- Slope charts
- Scatter plots (value labels are used in time scatters when scatterPointLabelStrategy is set to x or y)
Sig figs appear in the entity selector for consistency
Sig figs don't appear in the data table, here we always use fixed-point notation (note that numDecimalPlaces is respected here)