Markline position inside grid area

[Ovilia]

What problem does this feature solve?

Currently, if set the position of markLine to be "left" or "right", it will go outside of the grid area. This may cause some bad influence when the grid area is near the edge of the Canvas.
I hope to get new position options to make them be positioned like the following design:

What does the proposed API look like?

Previous valid values: 'start', 'middle', 'end'.
Proposed position names: 'start', 'middle', 'end', 'insideStartTop', 'insideStartBottom', 'insideMiddleTop', 'insideMiddleBottom', 'insideEndTop', 'insideEndBottom'.

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