internal/lsp: change names used by per-folder configs

This was causing microsoft/vscode-go#2749, which was a result of users
having folders named "go", and VSCode-Go returning the "go"
configuration settings (which are all of its settings, not those of
gopls).

Change-Id: Ifbde3e32ad2de79265ed6adea53588c730ecd716
Reviewed-on: https://go-review.googlesource.com/c/tools/+/196197
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>

internal/lsp/general.go

@@ -183,7 +183,7 @@ func (s *Server) fetchConfig(ctx context.Context, name string, folder span.URI,
 				Section:  "gopls",
 			}, {
 				ScopeURI: protocol.NewURI(folder),
-				Section:  name,
+				Section:  fmt.Sprintf("gopls-%s", name),
 			}},
 		},
 	}