fix(visualMap): fix some text style can't work on visualMap

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Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Fix some text style (width/overflow/align/verticalAlign...) can't work on visualMap (piecewise & continuous). This PR also improves the previous fix in #16679.

Fixed issues

• Resolves [Bug] width/overflow in visualMap.texStyle is not working #20956
• Resolves [Bug] visualMap.textStyle.overflow is not working #18882
• Resolves visualMap设置文字width无效 #15644

Details

Before: What was the problem?

After: How does it behave after the fixing?

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

See test/visualMap-pieces.html

Others

Merging options

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

Other information

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The changes brought by this PR can be previewed at: https://echarts.apache.org/examples/editor?version=PR-20961@7d76132