crypto/elliptic: use generics for nistec-based curves

There was no way to use an interface because the methods on the Point
types return concrete Point values, as they should.

A couple somewhat minor annoyances:

    - Allocations went up due to #48849. This is fine here, where
      math/big causes allocations anyway, but would probably not be fine
      in nistec itself.

    - Carrying the newPoint/newGenerator functions around as a field is
      a little weird, even if type-safe. It also means we have to make
      what were functions methods so they can access newPoint to return
      the zero value. This is #35966.

For #52182

Change-Id: I050f3a27f15d3f189818da80da9de0cba0548931
Reviewed-on: https://go-review.googlesource.com/c/go/+/360015
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

0 files changed, 0 insertions, 0 deletions