[sidshas03]

Fixes: #21834
Problem with nameMoveOverlap on, nameGap was applied before the overlap move. So small nameGap values all gave the same position, and the name only moved when the gap was bigger than the labels. You couldn't set a fixed gap from the labels.

What I did in AxisBuilder.ts, when nameMoveOverlap is on, the name now starts with no gap. After the overlap move is done, I add nameGap in the same direction. So nameGap: 10 always means 10px past the labels. Negative nameGap is ignored in this mode so the name doesn't go back on the labels. With nameMoveOverlap off, nothing changes. I also updated the nameGap and nameMoveOverlap comments in axisCommonTypes.ts to match.

• The document changes have been made in doc(axis): clarify nameGap with nameMoveOverlap echarts-doc#543

[echarts-bot]

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Document changes are required in this PR. Please also make a PR to apache/echarts-doc for document changes and update the issue id in the PR description. When the doc PR is merged, the maintainers will remove the PR: awaiting doc label.