internal/lsp: add titles to go mod tidy and update go.sum fixes

These were missing titles, which was showing up empty for users in the
VS Code UI and leading people not to trust the fixes.

Also did a find references on SuggestedFix to confirm that we always
set the title in other cases.

Fixes golang/go#43234

Change-Id: I8d0f272c383a2e1a364aefcec6650988d18d4fb4
Reviewed-on: https://go-review.googlesource.com/c/tools/+/278778
Trust: Rebecca Stambler <rstambler@golang.org>
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

internal/lsp/cache/mod_tidy.go

@@ -209,13 +209,15 @@ See https://github.com/golang/go/issues/39164 for more detail on this issue.`,
 				Message: `go.sum is out of sync with go.mod. Please update it or run "go mod tidy".`,
 				SuggestedFixes: []source.SuggestedFix{
 					{
+						Title: source.CommandTidy.Title,
 						Command: &protocol.Command{
 							Command:   source.CommandTidy.ID(),
 							Title:     source.CommandTidy.Title,
 							Arguments: args,
 						},
 					},
 					{
+						Title: source.CommandUpdateGoSum.Title,
 						Command: &protocol.Command{
 							Command:   source.CommandUpdateGoSum.ID(),
 							Title:     source.CommandUpdateGoSum.Title,