[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/video_core/buffer_cache/buffer_cache_base.h

@@ -16,7 +16,7 @@
 #include <span>
 #include <vector>
 
-#include <ankerl/unordered_dense.h>
+#include "common/container/unordered_map.h"
 #include <boost/container/static_vector.hpp>
 #include <boost/container/small_vector.hpp>
 

src/video_core/buffer_cache/memory_tracker_base.h

@@ -11,7 +11,7 @@
 #include <deque>
 #include <limits>
 #include <type_traits>
-#include <ankerl/unordered_dense.h>
+#include "common/container/unordered_set.h"
 #include <utility>
 
 #include "common/alignment.h"
@@ -257,7 +257,7 @@ private:
     std::array<Manager*, NUM_HIGH_PAGES> top_tier{};
     std::deque<std::array<Manager, MANAGER_POOL_SIZE>> manager_pool;
     std::deque<Manager*> free_managers;
-    ankerl::unordered_dense::set<u32> cached_pages;
+    ::Common::unordered_set<u32> cached_pages;
     DeviceTracker* device_tracker = nullptr;
 };