fix(DirectoryTree): selectedKeys updating

[doommm]

This is a ...

• New feature
• Bug fix
• Site / document update
• Component style update
• TypeScript definition update
• Refactoring
• Code style optimization
• Branch merge
• Other (about what?)

What's the background?

In multiple mode, on single click on tree node item, it should emit single value instead of multiple values.

See original implementation of ant-design: https://github.com/ant-design/ant-design/blob/8d05774053138e807755c616ba1cf3fa296200dd/components/tree/DirectoryTree.tsx#L160-L166

API Realization (Optional if not new feature)

1. Basic thought of solution and other optional proposal.
2. List final API realization and usage sample.
3. GIF or snapshot should be provided if includes UI/interactive modification.

What's the effect? (Optional if not new feature)

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2. What will say in changelog?
3. Does this PR contains potential break change or other risk?

Changelog description (Optional if not new feature)

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Self Check before Merge

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• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed

Additional Plan? (Optional if not new feature)

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