Update serialization for InspectorFrontendClient and PlatformTextTrackData to the new format
<rdar://problem/116098797>
Pull request: https://github.com/WebKit/WebKit/pull/18262
Committed 268507@main (77a5b5dffe62): <https://commits.webkit.org/268507@main> Reviewed commits have been landed. Closing PR #18262 and removing active labels.