Add option for labelled values on all chart plot types

[Chris Mitchell]

Pie chart has the option to position labels inside slices, but appears to be the only chart type that has label support.

It's common to want to show labels for chart series values for any chart type, esp. Column,Bar,Scatter,Line. We should consider this as a common feature.

For chart types with, properties are needed to specify location of the label, eg. inside/outside area, padding, alignment.

[cjolif]

#13403 is a duplicate of this ticket.

[cjolif]

tentative for 1.9

[cjolif]

first draft of patch to add labels on most plots that are missing them

[cjolif]

Note that pointing the mouse on the labels, prevents the columns to receive highlight or tooltip... I will come up with a workaround but having pointerEvents support in gfx (see #16370) would help.

[cjolif]

revised patch with some fixes + use in test sample

[cjolif]

In [30030]:

refs #11366. Implements labelling for Bubble/Columns/Default/Scatter?.

[cjolif]

In [30093]:

refs #11366. Fix issues with marker box.

[bill]

In [30102]:

fix syntax error from [30030] that breaks doc parser, refs #11366

[cjolif]

In [30273]:

refs #11366. Fix regression on v/hAxis positioning in markup as well as some space/tab issues

[cjolif]

In [30689]:

refs #11366. Fix regression on test_missingpoints.html introduced by [30030].

[subhajitbhuiya]

Can you please provide an example where individual bar is showing label / number? Which property to set for that.

[cjolif]

See in test_chart2d-amd.html, chart #24 (Clustered columns, custom axes, custom strokes, fills, and gap.), it is just setting labels: true property on the series.