[5.0] [Feature] support largest-triangle-three-buckets algo

[SnailSword]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Support largest-triangle-three-buckets sampling algorithm.

Fixed issues

#9403

Usage

Are there any API changes?

• The API has been changed.

sampling: 'lttb'

Related test cases or examples to use the new APIs

{
  type: 'line',
  sampling: 'lttb',
  data: data
}

See test/line-large.html line 101.

Others

Merging options

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

Other information

In master branch it works, see #13312.
But in next branch, because of #12997 , samplers doesn't run in some cases.
And when it run, there is a point highlight bug, I think it's better to fix those bugs in other pr.

[echarts-bot]

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[pissang]

Please don't use the code directly. It will have a license issue.

If you are sure that the code is definitely different. You should avoid using terms like copy from, Referencing, etc. in the comment.

[pissang]

Also, do you mind adding a test case to compare the result and performance difference between lttb sampling enabled and disabled?

The example used in #13314 (comment) will be a good case.

And there are some code style like inconsistent indentation needs to be fixed.

[SnailSword]

Also, do you mind adding a test case to compare the result and performance difference between lttb sampling enabled and disabled?

The example used in #13314 (comment) will be a good case.

@pissang Thank you for your advise. I added comparison of results in test/sample-compare.html. But I don't know how to compare the performance, time spent on this part(the pic below) is almost the same in each downsampling method, and also same as that without downsampling. I don't think it is the correct way to compare the performance.

And there are some code style like inconsistent indentation needs to be fixed.

Fixed.

[echarts-bot]

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