cmd/go/internal/get: use a strings.Replacer in expand
cmd/go/internal/get: use a strings.Replacer in expand

This should be a no-op, but produces deterministic (and more correct)
behavior if we have accidentally failed to sanitize one of the inputs.

Updates #29231

Change-Id: I1271d0ffd01a691ec8c84906c4e02d9e2be19c72
Reviewed-on: https://team-review.git.corp.google.com/c/370575
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@google.com>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@google.com>
Reviewed-on: https://go-review.googlesource.com/c/154103
Reviewed-by: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>

nawawi/go,nawawi/go,cloudflare/go,golang/go,akutz/go,akutz/go,golang/go,akutz/go,CAFxX/go,CAFxX/go,CAFxX/go,cloudflare/go,nawawi/go,nawawi/go,josharian/go,akutz/go,golang/go,golang/go,nawawi/go,golang/go,josharian/go,nawawi/go,cloudflare/go,CAFxX/go,nawawi/go,akutz/go,golang/go,cloudflare/go,josharian/go,CAFxX/go,josharian/go,josharian/go,CAFxX/go,nawawi/go,akutz/go,akutz/go,CAFxX/go,golang/go,josharian/go,CAFxX/go,cloudflare/go,cloudflare/go,josharian/go,golang/go,akutz/go,cloudflare/go,cloudflare/go,josharian/go