In preparation for making metadata immutable, move metadata-related
fields to a new MetadataGraph type. Other than instantiating this type
when cloning, this CL contains no functional changes.
For golang/go#45686
Change-Id: I7ad29d1f331ba7e53dad3f012ad7ecdae4f7d4b7
Reviewed-on: https://go-review.googlesource.com/c/tools/+/340730
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Rob Findley