use withAll when evaluating %foreign strings

[ear7h]

Description

The compiler was getting stuck when normalizing %foreign and %foreign_impl resulting in Error: %foreign calling convention must evaluate to a String. This was caused by getFnString using nf instead of nfOpts withAll which evaluates private names. This change reflects (heh) what's implemented in runElab:

Idris2/src/TTImp/ProcessRunElab.idr

Line 38 in 6ca00e7

nfstm <- nfOpts withAll defs env stm

Idris2/src/TTImp/Elab/RunElab.idr

Line 101 in 6ca00e7

nfOpts withAll defs env !(reflect fc defs False env tm)

Self-check

• This is my first time contributing, I've carefully read CONTRIBUTING.md
  and I've updated CONTRIBUTORS with my name.
• If this is a fix, user-facing change, a compiler change, or a new paper
  implementation, I have updated CHANGELOG_NEXT.md
• I confirm that this contribution did not involve GenerativeAI nor Large Language Models.