go/types: use internal/lazyregexp for goVersionRx

go/types: use internal/lazyregexp for goVersionRx

With benchinit, we see a noticeable improvement in init times:

	name     old time/op    new time/op    delta
	GoTypes    83.4µs ± 0%    43.7µs ± 1%  -47.57%  (p=0.029 n=4+4)

	name     old alloc/op   new alloc/op   delta
	GoTypes    26.5kB ± 0%    18.8kB ± 0%  -29.15%  (p=0.029 n=4+4)

	name     old allocs/op  new allocs/op  delta
	GoTypes       238 ± 0%       154 ± 0%  -35.29%  (p=0.029 n=4+4)

Port the same change to cmd/compile/internal/types and types2.

Updates #26775.

Change-Id: Ia1f7c4a4ce9a22d66e2aa9c9b9c341036993adca
Reviewed-on: https://go-review.googlesource.com/c/go/+/460544
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>