Add a copy of flag.PrintDefaults so that we can make changes.
This CL does not actually modify anything (although it does have
to detect the private stringValue type a slightly different way)
For #41860
Change-Id: I19512041f9c1bfde56226aea48302cd63cf670e2
Reviewed-on: https://go-review.googlesource.com/c/tools/+/367837
Trust: Ian Cottrell <iancottrell@google.com>
Run-TryBot: Ian Cottrell <iancottrell@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>