[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/am/frontend/applet_web_browser_types.h

@@ -7,7 +7,7 @@
 #pragma once
 
 #include <array>
-#include <ankerl/unordered_dense.h>
+#include "common/container/unordered_map.h"
 #include <vector>
 
 #include "common/common_funcs.h"
@@ -176,6 +176,6 @@ struct WebCommonReturnValue {
 };
 static_assert(sizeof(WebCommonReturnValue) == 0x1010, "WebCommonReturnValue has incorrect size.");
 
-using WebArgInputTLVMap = ankerl::unordered_dense::map<WebArgInputTLVType, std::vector<u8>>;
+using WebArgInputTLVMap = ::Common::unordered_map<WebArgInputTLVType, std::vector<u8>>;
 
 } // namespace Service::AM::Frontend