crypto/x509: don't panic marshaling invalid ECDSA keys

crypto/x509: don't panic marshaling invalid ECDSA keys

MarshalPKIXPublicKey, CreateCertificate, CreateCertificateRequest,
MarshalECPrivateKey, and MarshalPKCS8PrivateKey started raising a panic
when encoding an invalid ECDSA key in Go 1.19. Since they have an error
return value, they should return an error instead.

Fixes #54288

Change-Id: Iba132cd2f890ece36bb7d0396eb9a9a77bdb81df
Reviewed-on: https://go-review.googlesource.com/c/go/+/422298
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>