Fix playground sample config synchronization

[Patrick Ribbsaeter (patrickswedish)]

Summary

Preserve sample-specific preferredEmitter and compilerOptions values when loading samples in the TypeSpec Playground.

Root cause

Updating Monaco with external sample content calls setValue, which synchronously emits onDidChangeContent. The listener refs were updated in later React effects, so this event could invoke a stale onContentChange closure and overwrite the newly generated tspconfig with the previous Playground state.

Changes

• Update the Monaco listener refs before synchronizing external content into the editor model.
• Make the Monaco test double synchronously emit content-change events from setValue.
• Add regression coverage proving external sample updates are not reported through stale callbacks.
• Add the required Chronus release-note entry.

Fixes #11659.

Validation

• pnpm --filter @typespec/playground... build
• pnpm --filter @typespec/playground test — 59 passed
• pnpm --filter @typespec/playground lint
• Prettier check
• pnpm change verify
• git diff --check

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