Extract NameID with full text (including comments)

[lucasmrod]

Hi folks!

At Fleet we are attempting to replace our own SAML implementation with crewjam/saml.
One of our internal tests failed because of NameID extraction (crewjam/saml will remove any comments from the NameID field).

This PR fixes the issue using the approach Duo recommended for remediation:

If You Maintain a SAML Processing Library

The most obvious remediation here is ensuring your SAML library is extracting the full text of a given XML element when comments are present.

[lucasmrod]

Hi @crewjam! Let me know if you want me to open an issue to link this PR to.