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

[plainheart]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Don't bolder when the line width in the normal state is 0.

Fixed issues

N/A.

Details

If users specify the line width in the normal state as 0, the bolder logic should be skipped.

Usage

Are there any API changes?

• The API has been changed.

Related test cases or examples to use the new APIs

See test/line-boldWhenHover.html

Others

Merging options

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

Other information

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[plainheart]

@pissang Moreover, let's have a look at another case area-large.html. There is only one series and its data is large, for a better visual experience, should we also avoid the 'bolder' logic? 'bolder' is more suitable for multiple series with the blur scope.

[pissang]

@plainheart I think it will be definitely better. But I can't think of a general design to solve issues like this currently.

[echarts-bot]

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

[pissang]

@plainheart Or should we disable border on emphasis by default? I'm not sure which is better in a normal scenario.