Generate metadata.json for Azure services

[v-jiaodi]

fixes #3005

[Copilot]

Pull Request Overview

This PR adds metadata.json generation for Azure-flavored services by extracting the API and emitter versions and emitting the file alongside other outputs.

• Introduces getTypespecTsVersion to fetch the Typespec-TS emitter version
• Defines buildMetadataJson to create a metadata.json with apiVersion and/or emitterVersion
• Emits the metadata.json file in the Azure flavor path

Comments suppressed due to low confidence (2)

packages/typespec-ts/src/index.ts:364

• There are no unit tests covering the new buildMetadataJson logic. Consider adding tests to verify correct JSON output when apiVersion and/or emitterVersion are present or absent.

function buildMetadataJson() {

packages/typespec-ts/src/index.ts:503

• The buildMetadataJson builder is invoked twice for Azure flavor—once inside generateMetadataAndTest and again after it. Removing the redundant call will prevent duplicate file emissions or overwrites.

if (isAzureFlavor) {