fix(core): make getConnectedDataURL opts optional - #21736

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Makes the opts argument of echartsInstance.getConnectedDataURL actually optional, as the rest of the method already assumes.

Fixed issues

Details

Before: What was the problem?

Calling the documented public API with no argument always threw:

chart.getConnectedDataURL();

TypeError: Cannot read properties of undefined (reading 'type')
    at ECharts.getConnectedDataURL (src/core/echarts.ts:1026)

opts is declared optional and every other read of it inside the method is written
defensively, but the very first read is not:

getConnectedDataURL(opts?: {...}): string {
    // ...
    const isSvg = opts.type === 'svg';                             // <- throws
    // ...
    const dpr = (opts && opts.pixelRatio) || this.getDevicePixelRatio();   // guarded
    // ...
    return targetCanvas.toDataURL('image/' + (opts && opts.type || 'png'));// guarded
    // ...
    return this.getDataURL(opts);   // getDataURL does `opts = opts || {}`
}

So the method is internally inconsistent: the opts && guards further down and the
delegation to getDataURL (which normalizes opts itself) are unreachable for a
no-argument call, because line 1026 has already thrown. The failure does not depend
on whether the chart is connected, on the renderer, or on the environment.

After: How does it behave after the fixing?

opts is normalized once at the top, mirroring getDataURL:

opts = opts || {};

getConnectedDataURL(), getConnectedDataURL(undefined) and
getConnectedDataURL({...}) all behave as documented. The existing opts && ...
reads are left alone — they are now simply redundant rather than load-bearing.

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

Added test/ut/spec/api/getConnectedDataURL.test.ts: no argument, explicit
undefined, and an explicit options object. The first two fail on master; the
third passes before and after and is kept as a control.

npm run test, npx tsc --noEmit and eslint on the changed file all pass.

Merging options

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

Other information

This is a different problem from #19278, which is about the SVG branch of the same
method; this PR does not address that issue.