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What kind of change does this PR introduce?

Make a clear statement that angular compiler option enableI18nLegacyMessageIdFormat has no effect when used with @angular/build:application bundler

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
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• angular.dev application / infrastructure changes
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Other information

Option use in webpack builder - useLegacyIds = wco.tsConfig.options.enableI18nLegacyMessageIdFormat ?? true;

So I spent quite a few hours today trying to migrate application to angular 20 and it was hard to troubleshoot why IDs are being changed when extract-i18n is executed and how can I not lost project translations. Docs highlight that one can use enableI18nLegacyMessageIdFormat for backwards compatibility with old i18n ids (which were sha-like I believe).

But it is partially true - because the option itself works only with @angular-devkit/build-angular webpack bundler. Hope this note will help someone