tweak(line): tweak default line bolder logic.

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Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

This PR is intended to tweak the default bolder logic of the line series.

• The line won't be bolder again in emphasis state by default
• Only make line bolder when there are more than one series and emphasis.focus is enabled
• Or the user manually specify lineStyle.width as bolder

Please refer to #13501 and #13013 for more details.

Fixed issues

• fix(line): only bolder when line width in normal state is larger than 0. #13501 (comment)

Details

Before: What was the problem?

It's unnecessary for some cases to make the line bolder.
bolder is more suitable for multiple series with the blur scope.

After: How is it fixed in this PR?

See above.

Usage

Are there any API changes?

• The API has been changed.

The new semantic value bolder for emphasis.lineStyle.width brought by #13013 has not been added to the document yet.

Related test cases or examples to use the new APIs

test/area-large.html
test/line-boldWhenHover.html

Others

Merging options

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

Other information

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