[Feature] Bar charts: add more options for emphasis focus

[rooney]

What problem does this feature solve?

On stacked bar charts, sometimes I need to emphasize the hovered stack (not just 'self'), e.g:

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And its series-equivalent:

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And optionally (for completeness) everything in the hovered dataIndex:

What does the proposed API look like?

{ emphasis: { focus: 'stack' | 'stackSeries' | 'dataIndex' } }