fix(line): set default z/zlevel for temporary symbol to avoid warnings.

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Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Set default z & zlevel for the temporary symbol to avoid warnings.

Fixed issues

• Fixes [Bug] option正确配置，控制台出现黄色警告提示 #16639
• Fixes 折线图加上showSymbol:false，tootip触摸时会报出 #17220

Details

Before: What was the problem?

There is a warning log from the console when hovering on the chart

After: How does it behave after the fixing?

No warning log when hovering on the chart

Document Info

One of the following should be checked.

• This PR doesn't relate to document changes
• The document should be updated later
• The document changes have been made in apache/echarts-doc#xxx

Misc

ZRender Changes

• This PR depends on ZRender changes (ecomfe/zrender#xxx).

Related test cases or examples to use the new APIs

Please refer to the last case in test/line-case.html

Others

Merging options

• Please squash the commits into a single one when merging.

Other information

[echarts-bot]

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[echarts-bot]

Congratulations! Your PR has been merged. Thanks for your contribution! 👍