[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>

docs/Deps.md

@@ -80,7 +80,6 @@ Certain other dependencies will be fetched by CPM regardless. System packages *c
 * [httplib](https://github.com/yhirose/cpp-httplib) - if `ENABLE_UPDATE_CHECKER` or `ENABLE_WEB_SERVICE` are on
   * This package is known to be broken on the AUR.
 * [cpp-jwt](https://github.com/arun11299/cpp-jwt) 1.4+ - if `ENABLE_WEB_SERVICE` is on
-* [unordered-dense](https://github.com/martinus/unordered_dense)
 
 On amd64:
 
@@ -119,7 +118,7 @@ Now, install all deps:
 sudo emerge -a \
     app-arch/lz4 app-arch/zstd app-arch/unzip \
     dev-libs/libfmt dev-libs/libusb dev-libs/mcl dev-libs/sirit \
-    dev-libs/unordered_dense dev-libs/boost dev-libs/openssl dev-libs/discord-rpc \
+    dev-libs/boost dev-libs/openssl dev-libs/discord-rpc \
     dev-util/spirv-tools dev-util/spirv-headers dev-util/vulkan-headers \
     dev-util/vulkan-utility-libraries dev-util/glslang \
     media-gfx/renderdoc media-libs/libva media-libs/opus media-video/ffmpeg \
@@ -260,7 +259,7 @@ brew install molten-vk
 <details>
 <summary>FreeBSD</summary>
 
-As root run: `pkg install devel/cmake sdl3 devel/boost-libs devel/catch2 devel/libfmt devel/nlohmann-json devel/ninja devel/nasm devel/autoconf devel/pkgconf devel/qt6-base devel/qt6-charts devel/simpleini net/enet multimedia/ffnvcodec-headers multimedia/ffmpeg audio/opus archivers/liblz4 lang/gcc12 graphics/glslang graphics/vulkan-utility-libraries graphics/spirv-tools www/cpp-httplib devel/unordered-dense vulkan-headers quazip-qt6`
+As root run: `pkg install devel/cmake sdl3 devel/boost-libs devel/catch2 devel/libfmt devel/nlohmann-json devel/ninja devel/nasm devel/autoconf devel/pkgconf devel/qt6-base devel/qt6-charts devel/simpleini net/enet multimedia/ffnvcodec-headers multimedia/ffmpeg audio/opus archivers/liblz4 lang/gcc12 graphics/glslang graphics/vulkan-utility-libraries graphics/spirv-tools www/cpp-httplib vulkan-headers quazip-qt6`
 
 If using FreeBSD 12 or prior, use `devel/pkg-config` instead.
 
@@ -294,7 +293,7 @@ pkg_add cmake nasm git boost unzip--iconv autoconf-2.72p0 bash ffmpeg glslang gm
 <summary>DragonFlyBSD</summary>
 
 ```sh
-pkg install gcc14 git cmake unzip nasm autoconf bash pkgconf ffmpeg glslang gmake jq nlohmann-json enet spirv-tools sdl3 vulkan-utility-libraries vulkan-headers catch2 libfmt openssl liblz4 boost-libs cpp-httplib qt6-base qt6-charts quazip-qt6 unordered-dense libva-vdpau-driver libva-utils libva-intel-driver
+pkg install gcc14 git cmake unzip nasm autoconf bash pkgconf ffmpeg glslang gmake jq nlohmann-json enet spirv-tools sdl3 vulkan-utility-libraries vulkan-headers catch2 libfmt openssl liblz4 boost-libs cpp-httplib qt6-base qt6-charts quazip-qt6 libva-vdpau-driver libva-utils libva-intel-driver
 ```
 
 [Caveats](./Caveats.md#dragonflybsd).
@@ -328,7 +327,7 @@ sudo pkgin install git cmake autoconf build-essential libusb-1 nasm gcc13
 
 ```sh
 BASE="git make autoconf libtool automake-wrapper jq patch"
-MINGW="qt6-base qt6-charts qt6-tools qt6-translations qt6-svg cmake toolchain clang python-pip openssl vulkan-memory-allocator vulkan-devel glslang boost fmt lz4 nlohmann-json zlib zstd enet opus libusb unordered_dense openssl SDL3"
+MINGW="qt6-base qt6-charts qt6-tools qt6-translations qt6-svg cmake toolchain clang python-pip openssl vulkan-memory-allocator vulkan-devel glslang boost fmt lz4 nlohmann-json zlib zstd enet opus libusb openssl SDL3"
 # Either x86_64 or clang-aarch64 (Windows on ARM)
 packages="$BASE"
 for pkg in $MINGW; do

docs/dynarmic/README.md

@@ -308,32 +308,6 @@ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
 ```
 
-### unordered_dense
-
-```
-MIT License
-
-Copyright (c) 2022 Martin Leitner-Ankerl
-
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
-
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.
-```
-
 ### xbyak
 
 ```