(1) Fix some buggy display result in tooltip, like 2 value axis scatter, add add test cases for them.
(2) Buggy results in tooltip.renderModel: 'richText' for each cases. And add test cases for them.
(3) Add styles to renderMode: 'richText', make them the same as renderMode: 'html'.
(4) Make `tooltip.confine` default `true` if `tooltip.renderMode` is `richText`. And fix the positioning of it to avoid to overflow the container, which will be cut.
(5) Fix the `tooltip.formatter` callback in `renderMode: 'richText'`, previously the concatenating rich text by `params.marker.content` does not work.
(6) Refactor the implementation of `Series['formatTooltip']`:
Add a abstract layer named `TooltipMarkup` to describe the tooltip layout requirement for each series,
instead of lots of messy code to concatenate `html` and `richText` in each series.
`TooltipMarkup` is responsible for generating `html` or `richText` finally.
Add `TooltipMarkup` is also in charge of sort the tooltip by `valueAsc`, `valueDesc`, `seriesAsc`, `seriesDesc`.

[TEST_CASES]: test/new-tooltip.html
[PENDING]: Do we need to expose API (like `tooltipMarkup.ts#TooltipMarkupStyleCreator`) to `tooltip.formatter` callback, by which users can add richText style themselves. At present users is not able to do that.
But if we expose that kind of API, there is an issue:
should we use ZRender style (use `fill` to describe text color)
or ECharts label style (use `color` to describe text color).

And add rule "no-var" to eslintrc

Use eslint rule to check the diff between var and let:
    "no-use-before-define": "off"
    "@typescript-eslint/no-use-before-define": 2
    no-redeclare: 2
    block-scoped-var: 2
    no-loop-func: 2
(2) By the way add some eslint rule and unify some code style.