fix(plugin-chart-echarts): drop locales not shipped by echarts 5.6.0

Greek (langEL) and Latvian (langLV) i18n bundles were added in echarts 6,
so the static locale import map fails to resolve them once the dependency
is pinned back to 5.6.0, breaking every webpack build. Both locales now
fall back to English, which loadLocale already handles.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: sadpandajoe

superset-frontend/plugins/plugin-chart-echarts/src/components/Echart.tsx

@@ -130,8 +130,11 @@ use([
 // code-split exactly the locales listed here. Keys are Superset locales
 // uppercased (see LANGUAGES in superset/config.py); values point at the
 // echarts bundle, whose naming differs for some locales (Slovenian is
-// langSI, Brazilian Portuguese is langPT-br). Superset locales absent
-// from this map fall back to English.
+// langSI, Brazilian Portuguese is langPT-br). Only locales that echarts
+// 5.6.0 ships a bundle for are listed — Greek (langEL) and Latvian
+// (langLV) were added in echarts 6 and must stay out until this
+// dependency is upgraded again. Superset locales absent from this map
+// fall back to English.
 type EChartsLocaleOption = Parameters<typeof registerLocale>[1];
 
 const LOCALE_LOADERS: Record<
@@ -141,7 +144,6 @@ const LOCALE_LOADERS: Record<
   AR: () => import('echarts/i18n/langAR.js'),
   CS: () => import('echarts/i18n/langCS.js'),
   DE: () => import('echarts/i18n/langDE.js'),
-  EL: () => import('echarts/i18n/langEL.js'),
   EN: () => import('echarts/i18n/langEN.js'),
   ES: () => import('echarts/i18n/langES.js'),
   FA: () => import('echarts/i18n/langFA.js'),
@@ -151,7 +153,6 @@ const LOCALE_LOADERS: Record<
   IT: () => import('echarts/i18n/langIT.js'),
   JA: () => import('echarts/i18n/langJA.js'),
   KO: () => import('echarts/i18n/langKO.js'),
-  LV: () => import('echarts/i18n/langLV.js'),
   NL: () => import('echarts/i18n/langNL.js'),
   PL: () => import('echarts/i18n/langPL.js'),
   RO: () => import('echarts/i18n/langRO.js'),