internal/lsp: cleanup temporary go.mod file on shutdown

This commit will delete the temporary go.mod file that is attached
to a view when the session is shutdown.

Updates golang/go#31999

Change-Id: I0f6b0663b0a814ce45d9b12468669f415f8c36aa
Reviewed-on: https://go-review.googlesource.com/c/tools/+/212479
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
Run-TryBot: Rohan Challa <rohan@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

internal/lsp/cache/view.go

@@ -304,6 +304,9 @@ func (v *view) shutdown(context.Context) {
 		v.cancel()
 		v.cancel = nil
 	}
+	if v.modfiles != nil {
+		os.Remove(v.modfiles.temp)
+	}
 	debug.DropView(debugView{v})
 }