Move generic containers into core/containers

[Spartan322]

• Incremental refactor to achieve Refactor types and utility directories to core #625

Move tracked allocating containers to memory namespace

HasIdentifier.hpp will be split into distinct class headers after merge following #625, done to focus on changing the namespace and headers and minimize refactoring header inclusions in this PR.

[wvpm]

Prefixing commonly used types with memory:: hurts code.
If you want to bring your own allocator, you'd be better off using _detail::T<MyAllocator>

No

[wvpm]

We could revive this. I am strongly in favour of splitting up Containers.hpp as it's leaking imports everywhere.
I still oppose prefixing commonly used types with memory::, especially if there is a variant without that prefix.

[wvpm]

Partially superseded by #731