feat(toolbox): expose toolbox feature extension API

[DaZuiZui]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Exposes a stable toolbox-feature registration API for independently packaged ECharts extensions.

Fixed issues

• [Feature] Support exporting chart data to CSV #21693: provides the core extension point required by the proposed independent export-toolbox package; the exporter package itself remains outside ECharts core.

Details

Before: What was the problem?

Toolbox features are stored in an internal registry. ECharts extensions installed with echarts.use() cannot access that registry, and the public custom-feature path only recognizes option keys prefixed with my. As a result, an independent package cannot register a first-class feature such as toolbox.feature.exportData without importing internal modules.

After: How does it behave after the fixing?

The extension installer now exposes registerToolboxFeature(name, ctor). ToolboxFeature and its option/model/constructor types, together with the extension installer types, are exported from echarts/core.

An external package can now register a feature through the normal extension lifecycle:

class ExportDataFeature extends ToolboxFeature<ExportDataFeatureOption> {
    onclick(): void {
        // Delegate to the package's shared programmatic exporter.
    }
}

const install: EChartsExtensionInstaller = (registers) => {
    registers.registerToolboxFeature('exportData', ExportDataFeature);
};

echarts.use(install);

The change adds no exporter implementation or third-party dependency to ECharts core. CSV/PDF/XLSX implementations can remain independently packaged and tree-shakeable.

Document Info

• 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

• Unit coverage verifies registration through echarts.use().
• Public DTS coverage verifies subclassing ToolboxFeature and calling registerToolboxFeature from echarts/core.
• npm run checktype
• Targeted Jest and ESLint checks
• DTS tests with TypeScript 4.7 through 5.9

Merging options

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

Other information

The matching independent exporter prototype uses explicit table / getTable(chart) data sources and shares one exporter registry between its toolbox and programmatic APIs, as described in #21693.

[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.

Please DO NOT commit the files in dist, i18n, and ssr/client/dist folders in a non-release pull request. These folders are for release use only.

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.