fix(plugin-chart-echarts): import the -obj locale build so time axes render

[sadpandajoe]

SUMMARY

Every chart with a temporal x-axis (line, area, bar, ...) throws
TypeError: Cannot read properties of null (reading '0') while rendering axis labels.

echarts ships two UMD builds per locale:

file	behaviour
echarts/i18n/langEN.js	self-registers under echarts' own key, exports nothing
echarts/i18n/langEN-obj.js	exports the locale object

Echart.tsx imported the first one, so (await loader()).default was {} — empty, but
truthy, so it passed the if (localeObj) guard and got handed to registerLocale('EN', {}).
That call overwrote the complete locale the very same module had just self-registered,
leaving the registered locale with no time section.

echarts' formatTime builds its result as a chained .replace(), and replacement
arguments are evaluated eagerly — it reads month[u - 1] even when the template is
just {yyyy}. With time missing, month is null and every single axis label throws.

The fix switches all 24 loaders to the -obj.js build, and additionally refuses to register
a locale object that has no time section, so a future bad import degrades to echarts'
built-in locale instead of crashing the chart.

This also stops dragging the full echarts bundle in: the langXX.js CJS branch does
require('echarts/lib/echarts'), which defeats the tree-shaken echarts/core setup this
plugin uses. The -obj factory takes only exports. (Improvement expected, not measured.)

Regression origin

echarts/lib/i18n/lang${locale} (a real ESM module with a full export default) was
swapped for echarts/i18n/lang${locale}.js in #42055, and that path was then carried
forward into the static LOCALE_LOADERS map in #42154. The defect is independent of the
echarts major version — 5.6.0 and 6.1.0 both ship the same two i18n flavours.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

1. Open any chart with a temporal x-axis (e.g. a line chart from the sample data).
2. Before this change the chart fails to render and the console shows
   Cannot read properties of null (reading '0') from echarts' formatTime.
   After this change the chart renders with formatted time axis labels.
3. Repeat with a non-English locale to confirm localized labels still work.

Automated:

cd superset-frontend
npm run test -- plugins/plugin-chart-echarts

A new test in test/components/Echart.test.tsx asserts the object handed to
registerLocale actually carries a 12-entry time.month, which fails against the
previous import path.

ADDITIONAL INFORMATION

• Has associated issue:
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• Includes DB Migration (follow approval process in SIP-59)
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• Removes existing feature or API

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Review Details

• Files reviewed - 2 · Commit Range: 22d8e30..22d8e30

  • superset-frontend/plugins/plugin-chart-echarts/src/components/Echart.tsx
  • superset-frontend/plugins/plugin-chart-echarts/test/components/Echart.test.tsx
• Files skipped - 0
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Codecov Report

❌ Patch coverage is 11.53846% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 65.25%. Comparing base (641713f) to head (22d8e30).

Files with missing lines	Patch %	Lines
...ins/plugin-chart-echarts/src/components/Echart.tsx	11.53%	23 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #42317   +/-   ##
=======================================
  Coverage   65.25%   65.25%           
=======================================
  Files        2793     2793           
  Lines      157251   157252    +1     
  Branches    35947    35948    +1     
=======================================
+ Hits       102611   102612    +1     
  Misses      52663    52663           
  Partials     1977     1977           

Flag	Coverage Δ
javascript	71.14% <11.53%> (+<0.01%)	⬆️

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