Replaces all instances of ankerl's unordered map/set with boost's
`unordered_flat_*` classes. This uses std::hash since boost::hash is
actually a lot slower.
Also adds an abstraction layer in `Common` so future changes are quicker
and easier.
Other implementation details:
- ankerl provided hash specializations for tuple and pair, so those were
ported here
- std::erase_if doesn't work on boost, so just used the ADL'd erase_if
This should be about equal or superior performance as unordered_dense for everything except iteration.
Signed-off-by: crueter <crueter@eden-emu.dev>
- [x] I have read and followed the [Contribution Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/CONTRIBUTING.md#code-contributions).
- [x] I have read and followed the [AI Policy](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/AI.md)
- [x] I have read and followed the [Coding Guidelines](https://git.eden-emu.dev/eden-emu/eden/src/branch/master/docs/policies/Coding.md) to the best of my ability.
-------------------
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/4326
Reviewed-by: Lizzie and Samuel <lizzie@eden-emu.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
crueter