Having merged #1942 (from which all of this work is derived), this makes the BaseValue and BaseLine consistent across all the 'bar-type' series, and exposes the ActualBaseLine as a { public get; protected set; } property.

Checklist

• I have included examples or tests
• I have updated the change log
• I am listed in the CONTRIBUTORS file
• I have cleaned up the commit history (use rebase and squash)

Changes

• All 3 series have consistent support for negative values, determined by a BaseValue that defaults to zero.
• Fixes issues with rendering against log axes by explicit detection and use of YAxis.ClipMinimum to clamp to end of plot
• All 3 series have consistent support for a BaseLine which is included in the Y-axis: important for log-axes which extend to infinity that they have a sensisble 'reference' baseline. When NaN, actual value is derived for log-axes by dividing the smallest value by 10 (to give some padding to log plots: better ideas welcome (e.g. depend on range of values and base of axis?): computed values is exposed as ActualBaseLine

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