Use the FullDocumentation hover response instead of Structured, becausethe latter is deprecated and will be removed soon.* Parse FullDocumentation format for use in a hover message, following  the same basic format was was previously provided by gopls in its  Structured format.* Refactor handlers that relied on the hover response to expect the  structured output from the new function that provides it.* Refactor functions that expected documentation links to first rely on  a new request, documentLink via go#lsp#DocLink, and then falling back  to trusty `go doc` to get what's needed.