1. -maxsigcachesize is a DEBUG_ONLY option
2. Almost 7 years has passed since its semantics change in
830e3f3d027ba5c8121eed0f6a9ce99961352572 from "number of entries" to
"number of mebibytes"
3. A std::new_handler was added to the codebase after the original PR
which introduced this limit, which will terminate immediately instead
of causing trouble by being caught somewhere unexpected.
This is a partial backport of core#25527
https://github.com/bitcoin/bitcoin/pull/25527/commits/b370164b319df1a500b70694b077f92265a777fb
Depends on D15735