[clang-tidy] Match InitListExpr in modernize-use-default-member-init

Summary:
modernize-use-default-member-init wasn't warning about redundant initialisers
when the initialiser was an InitListExpr.  Add initListExpr to the matcher.

Fixes: PR44439

Reviewers: aaron.ballman, alexfh, JonasToth

Reviewed By: aaron.ballman

Subscribers: xazax.hun, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D72691