Unfortunately, the HashWithIndifferent access approach is insufficient
for our needs. It's perfectly reasonable to want to use keyword
arguments with Active Job, which we will see as a symbol keyed hash. For
Ruby to convert this back to keyword arguments, it must deserialize to a
symbol keyed hash.

There are two primary changes to the serialization behavior. We first
treat a HWIA separately, and mark it as such so we can convert it back
into a HWIA during deserialization.

For normal hashes, we keep a list of all symbol keys, and convert them
back to symbol keys after deserialization.

Fixes #18741.

Conflicts:
	activejob/CHANGELOG.md