Remove 1 usage of Protocol.Emulation.UserAgentMetadata
Remove 1 usage of Protocol.Emulation.UserAgentMetadata

Protocol.Emulation.UserAgentMetadata has a superset of the properties we
need here, and eliminating usage of Protocol types is favorable because
CDP types are more likely to change than a web platform API like
WorkerNavigator.

WorkerNavigator.userAgentData is standardized but realtively new, so we
can make typescript happy by extending the Navigator interface to include
it.

Bug: none
Change-Id: I48b760f2329dd95ca6a7926e613449ec753fbd34
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/3665438
Commit-Queue: Olivia Flynn <e15af8a2a383aadd6a5ccd799ab5978af5fa4a94@microsoft.com>
Reviewed-by: Danil Somsikov <f16a5ee11618cab93684e694f9aa762d34f02920@chromium.org>

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