refactor: use C++11 default initializers
Summary:
This is a backport of core#25108
Depends on D18661
Test Plan:
cmake .. -GNinja -DBUILD_CHRONIK=1 -DENABLE_CLANG_TIDY=ON -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ ninja all check bitcoin-fuzzers bitcoin-bench
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D18662