Heatmap axis label render bad with small multiples

[nickofthyme]

Describe the issue

When a user goes to create a heatmap split chart on the agg-based vis library with only an xAccessor. If they do not specify a yAccessor bucket, the labels of the split will be rendered on top of the chart.

Expected behaviour

Axis labels are rendered correctly on the correctly sized axis

Screenshots

Notice the axis label of the small multiple on the left vertical axis

Version (please complete the following information):

• Elastic Charts: v55.0.0

Additional context

Only happens with no xAccessor and no value is passed to yAxisTitle.

Kibana Cross Issues

elastic/kibana#176265