[common] Switch to boost::unordered_flat containers (#4326)

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>

src/core/hle/service/ldn/lan_discovery.h

@@ -15,7 +15,7 @@
 #include <random>
 #include <span>
 #include <thread>
-#include <ankerl/unordered_dense.h>
+#include "common/container/unordered_map.h"
 
 #include "common/logging.h"
 #include "common/socket_types.h"
@@ -119,7 +119,7 @@ protected:
     std::array<LanStation, StationCountMax> stations;
     std::array<NodeLatestUpdate, NodeCountMax> node_changes{};
     std::array<u8, NodeCountMax> node_last_states{};
-    ankerl::unordered_dense::map<MacAddress, NetworkInfo, MACAddressHash> scan_results{};
+    ::Common::unordered_map<MacAddress, NetworkInfo, MACAddressHash> scan_results{};
     NodeInfo node_info{};
     NetworkInfo network_info{};
     State state{State::None};