add missing js doc comment descriptions for hydrogen 2025-07 gen docs v1

[laurelthorburn]

WHY are these changes introduced?

Part of https://github.com/shop/issues-learn/issues/1460

Shopify-dev PR: https://github.com/shop/world/pull/547474

After merging the gen docs v1 migration, some JSDoc comments on types/interfaces/functions were missing or didn't match their corresponding .doc.ts definition descriptions. This caused descriptions to not show up correctly in the generated docs UI.

WHAT is this pull request doing?

Fixes JSDoc comments to match .doc.ts definition descriptions in hydrogen-react and hydrogen packages (2025-07 branch):

Description mismatches (JSDoc had wrong text):

• ExternalVideoBaseProps in ExternalVideo.tsx — was using the component description instead of the props description
• getClientBrowserParameters in analytics.ts — updated to match .doc.ts definition description
• parseMetafield in parse-metafield.ts — updated to match .doc.ts definition description

HOW to test your changes?

1. Run npm run build to confirm no build errors
2. Run docs generation and verify the descriptions now appear correctly in the generated docs output for the affected pages

Post-merge steps

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or functional changes. Test changes or internal-only config changes do not require a changeset.
• I've added tests to cover my changes
• I've added or updated the documentation

[github-actions]

We detected some changes in packages/*/package.json or packages/*/src, and there are no updates in the .changeset.
If the changes are user-facing and should cause a version bump, run npm run changeset add to track your changes and include them in the next release CHANGELOG.
If you are making simple updates to examples or documentation, you do not need to add a changeset.