fix(line): keep labels above lines. close #15679

[rahul37wallst-sudo]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Keeps line series paths below labels from mixed series by lowering the default line polyline z2.

Fixed issues

• Line graph overlaps labels on other series on mixed series #15679: Line graph overlaps labels on other series on mixed series.

Details

Before: What was the problem?

In mixed charts such as bar + line, the line polyline used a default z2 of 10.

That made the line path render above labels attached to other series, so a line series could visually overlap bar labels.

After: How does it behave after the fixing?

The line polyline default z2 is lowered to 1, so it no longer sits above labels from other series.

A regression test was added to verify that a line polyline is rendered below a bar label in a mixed bar + line chart.

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

Security Checking

• This PR uses security-sensitive Web APIs.

ZRender Changes

• This PR depends on ZRender changes (ecomfe/zrender#xxx).

Related test cases or examples to use the new APIs

• test/ut/spec/series/line.test.ts

Validation run:

• npx jest --config test/ut/jest.config.cjs --coverage=false --runInBand --runTestsByPath test/ut/spec/series/line.test.ts
• npm run lint
• npm run checktype
• npx eslint test/ut/spec/series/line.test.ts
• git --no-pager diff --check

Merging options

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

Other information

N.A.