feat: support auto computing dark mode

[Ovilia]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Currently, dark mode is a manually configured theme in Apache ECharts. It's troublesome to make another theme and making it consistant with the light theme as well as adjusting to make sure there is enough contrast between the foreground and the background.

In this PR, I propose a method to convert to dark mode without extra designing and developing.

See zrender#1093 for more.

Document Info

One of the following should be checked.

• This PR doesn't relate to document changes
• The document should be updated later
• The document changes have been made in apache/echarts-doc#xxx

Misc

ZRender Changes

• This PR depends on ZRender changes (feat: support auto computing dark mode ecomfe/zrender#1093).

Related test cases or examples to use the new APIs

N.A.

Others

Merging options

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

Other information

[echarts-bot]

Thanks for your contribution!
The community will review it ASAP. In the meanwhile, please checkout the coding standard and Wiki about How to make a pull request.

The pull request is marked to be PR: author is committer because you are a committer of this project.

Document changes are required in this PR. Please also make a PR to apache/echarts-doc for document changes and update the issue id in the PR description. When the doc PR is merged, the maintainers will remove the PR: awaiting doc label.

This PR depends on ZRender changes. Please update the ZRender dependency to the latest nightly version including this change, which takes place everyday at 8:00 UTC (16:00 Beijing Time).
You can use npm i zrender@npm:zrender-nightly@dev to update package.json.
If you have any question about this, please leave a comment and we will give you extra help on this.