Fix some common anti-patterns with these data structures.
- You can dereference the iterator returned by `find` to access the
underlying value directly, without an extra `operator[]`/`at`.
- Rather than checking for an element before insertion/deletion, you can
just do the operation and if needed check the return value to
determine if the insertion/deletion succeeded.
In PPCTables.cpp, the code is currently unused so I was unable to test it.
In CustomPipeline.cpp, a pointer to member function cannot be used due to 16.4.5.2.1 of the C++ Standard regarding "addressable functions". https://eel.is/c++draft/namespace.std#6
In Fs.cpp and DirectoryBlob.cpp, these examples used projections in a previous iteration of this commit, but no longer do. Still, they remain in this commit because the PR they would actually belong to is already merged.
In NandPaths.cpp, the `std::initializer_list<char>` of illegal characters has been turned into a `char[]` (similar to the one in GameList.cpp).
The reverse iteration in ResourcePack.cpp seemed to provide no benefits, and doing without it it seemed to have no ill effects.
Instead, we make the event take a reference to the system and then pass
it in when the event is triggered.
This does introduce two other accessors, but these are much easier to
refactor out over time, and without modification to the existing event
interface.
