CancelEdit function

**maptalks's version and what browser you use?**
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0.46.0

**Issue description**
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It would be great to have "cancelEdit" function to move history pointer to the beginning. For now, we can use "undoEdit" n times to get the cancel edit result, but it doesn't seem to be the right way. Tell me if I'm wrong :)

**Please provide a reproduction URL (on any jsfiddle like site)**
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