Feature #7340. Add the itemStyle to legend

[yufeng04]

Add the itemStyle to legend symbol.

• The default borderWidth of legend symbol is 0, so the borderColor only can be seen when the legend.itemStyle.borderWidth isn't 0.
• legend.itemStyle.borderWidth !== 0
  1. the borderWidth of legend symbol only depends on legend.itemStyle.borderWidth
  2. the boderColor of legend symbol depends on legend.itemStyle.borderColor and series[i].itemStyle.borderColor, and the legend.itemStyle.borderColor has higher priority.
  3. The borderColor of emptyCircle legend symbol is the same as color of series
  4. The legend borderColor is incompatible with barBorderColor
• The former PR

[100pah]

itemModel should not be created twice if both singleDataborderColor and singleDataColor is true.

[yufeng04]

Thanks！I didn't take this into account.

[100pah]

Why they are different

[yufeng04]

The emptyCircle symbol doesn't have fillColor, so the strokeColor should be the same as color of corresponding series

[100pah]

If use scatter:
If symbol: emptyCircle: The color of scatter is different with legend.
If symbol: circle border set, legend do not show the border.

var option4 = {
    tooltip: {
        trigger: 'axis',
        axisPointer: {
            type: 'shadow'
        }
    },
    legend: {
        // itemStyle: {
        //     borderWidth: 3
        // },
        // selected: {
        //     '联盟广告': false
        // }
    },
    grid: {
        left: '3%',
        right: '4%',
        bottom: '3%',
        containLabel: true
    },
    xAxis: [
        {
            type: 'category',
            data: ['周一', '周二', '周三', '周四', '周五', '周六', '周日']
        }
    ],
    yAxis: [
        {
            type: 'value'
        }
    ],
    series: [
        {
            name: '直接访问',
            type: 'scatter',
            data: [320, 332, 301, 334, 390, 330, 320],
            symbol: 'emptyCircle',
            itemStyle: {
                borderColor: '#5e1',
                borderWidth: 3
            }
        },
        {
            name: '邮件营销',
            type: 'scatter',
            data: [120, 132, 101, 134, 90, 230, 210],
            symbol: 'emptyCircle',
            itemStyle: {
                borderColor: '#ae2',
                borderWidth: 5
            }
        },
        {
            name: '邮件营销2',
            type: 'scatter',
            data: [21, 33, 11, 22, 22, 11, 22],
            symbol: 'circle',
            itemStyle: {
                borderColor: '#912',
                borderWidth: 5
            }
        }
    ]
};
// chart1.setOption(option4);
testHelper.create(echarts, 'plain4', {
    title: [
        '(Legend symbol of line)??',
    ],
    option: option4,
    height: 300
});

[yufeng04]

The default borderWidth of legend symbol is 0, so the borderColor only can be seen when the legend.itemStyle.borderWidth is not 0.