x509asn1: add some common ECDSA OIDs

[Bo98]

ecdsa-with-SHA256 and ecdsa-with-SHA384 are used by GitHub.com's certificate chain

See #13845

[bagder]

Do we actually need this once we merge #13858?

[Bo98]

It's not necessary in order to fix #13845, but I think it still has some value in that it slightly improves the output of curl -w '%{certs}'.

Before (assuming #13858 already is applied):

Signature Algorithm:1.2.840.10045.4.3.2

After:

Signature Algorithm:ecdsa-with-SHA256

Which is consistent with what we already do for RSA certs:

Signature Algorithm:sha384WithRSAEncryption

and with how it is displayed for other SSL backends that do OID mapping themselves.

So I'd see #13858 as the real bugfix for #13845 and this PR as a cosmetic enhancement for ECDSA certs.

[bagder]

Lovely, thanks!