refactor: index: use AbortNode in fatal error helper

Summary:
Deduplicates code in the FatalError template function by using
AbortNode which does the exact same thing if called without any user
message (i.e. without second parameter specified). The template is still
kept for ease-of-use w.r.t. not having to call tfm::format(...) at the
call-side each time, and also to keep the diff minimal.

This is a partial backport of core#27708
https://github.com/bitcoin/bitcoin/pull/27708/commits/3c06926cf21dcca3074ef51506f556b2286c299b

Depends on D18596

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18597