WIP(legend): more intuitive legend design

[Ovilia]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Update default legend style so that the icons looks more intuitively like that of the series.

Fixed issues

Details

Before: What was the problem?

Legend for line series only have the color of the series, lacking itemStyle.borderWidth, itemStyle.borderColor, lineStyle.color, lineStyle.borderColor and etc.

After: How is it fixed in this PR?

Legend for line series looks more like that of the series.
emptyCircle has been changed to circle.

See test/legend-style.html for more info.

Usage

Are there any API changes?

• The API has been changed.

symbol of emptyCircle has been deprecated.

Related test cases or examples to use the new APIs

test/legend-style.html

TODO

• Compat emptyCircle in other cases
• Support other series (scatter series and etc.)

Others

Merging options

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

Other information

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[Ovilia]

Too many conflicts. Close this PR and open a new open later.