Introduce vcpkg for dependency management

* Manually including libraries into the project while a perfectly acceptable solution
  leads to slow updates and large maintainance costs. To address this
  shortcoming we are introducing a package manager namely vcpkg into the
  codebase to handle the download and build of most external dependencies. Conan
  was also considered but vcpkg was chosen due to the centralized nature
  of the project. To achieve the integration the CMake configuration has
  been altered but not by much:

  1. Packages handled by vcpkg have been moved from
     externals/CMakeLists.txt to the root one to make them available to
     all subdirectories.

  2. In addition now find_package is used in accordance to the vcpkg
     recommendations.

  3. All libraries built by vcpkg have been updated to their latest
     available version, except for Qt because our codebase isn't
     compatible with Qt 6.0 yet.

  Currently there are build issues caused by the fmtlib upgrade.
  Another question is how to handle large libraries like Qt, Boost and
  SDL2 which will be addressed in a later commit.

externals/CMakeLists.txt

@@ -9,34 +9,6 @@ set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${PROJECT_SOURCE_DIR}/CMakeModules)
 include(DownloadExternals)
 include(ExternalProject)
 
-# Boost
-set(BOOST_ROOT "${CMAKE_SOURCE_DIR}/externals/boost")
-set(Boost_INCLUDE_DIR "${CMAKE_SOURCE_DIR}/externals/boost")
-set(Boost_NO_SYSTEM_PATHS ON)
-add_library(boost INTERFACE)
-target_include_directories(boost SYSTEM INTERFACE ${Boost_INCLUDE_DIR})
-
-# Boost::serialization
-file(GLOB boost_serialization_SRC "${CMAKE_SOURCE_DIR}/externals/boost/libs/serialization/src/*.cpp")
-add_library(boost_serialization STATIC ${boost_serialization_SRC})
-target_link_libraries(boost_serialization PUBLIC boost)
-
-# Add additional boost libs here; remember to ALIAS them in the root CMakeLists!
-
-# Catch
-add_library(catch-single-include INTERFACE)
-target_include_directories(catch-single-include INTERFACE catch/single_include)
-
-# Crypto++
-add_subdirectory(cryptopp)
-
-# Xbyak
-if (ARCHITECTURE_x86_64)
-    add_library(xbyak INTERFACE)
-    target_include_directories(xbyak SYSTEM INTERFACE ./xbyak/xbyak)
-    target_compile_definitions(xbyak INTERFACE XBYAK_NO_OP_NAMES)
-endif()
-
 # Dynarmic
 if (ARCHITECTURE_x86_64 OR ARCHITECTURE_ARM64)
     set(DYNARMIC_TESTS OFF)
@@ -45,18 +17,11 @@ if (ARCHITECTURE_x86_64 OR ARCHITECTURE_ARM64)
     add_subdirectory(dynarmic)
 endif()
 
-# libfmt
-add_subdirectory(fmt)
-add_library(fmt::fmt ALIAS fmt)
-
 # getopt
 if (MSVC)
     add_subdirectory(getopt)
 endif()
 
-# Glad
-add_subdirectory(glad)
-
 # inih
 add_subdirectory(inih)
 
@@ -79,68 +44,13 @@ target_include_directories(SoundTouch INTERFACE ./soundtouch/include)
 # Teakra
 add_subdirectory(teakra EXCLUDE_FROM_ALL)
 
-# Zstandard
-add_subdirectory(zstd/build/cmake EXCLUDE_FROM_ALL)
-target_include_directories(libzstd_static INTERFACE $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}/externals/zstd/lib>)
-
-# ENet
-add_subdirectory(enet)
-target_include_directories(enet INTERFACE ./enet/include)
-
 # Cubeb
 if (ENABLE_CUBEB)
     set(BUILD_TESTS OFF CACHE BOOL "")
     add_subdirectory(cubeb EXCLUDE_FROM_ALL)
 endif()
 
-# DiscordRPC
-if (USE_DISCORD_PRESENCE)
-    add_subdirectory(discord-rpc EXCLUDE_FROM_ALL)
-    target_include_directories(discord-rpc INTERFACE ./discord-rpc/include)
+if (ENABLE_WEB_SERVICE AND ANDROID)
+    add_subdirectory(android-ifaddrs)
 endif()
 
-if (ENABLE_WEB_SERVICE)
-    find_package(OpenSSL 1.1)
-    if (OPENSSL_FOUND)
-        set(OPENSSL_LIBRARIES OpenSSL::SSL OpenSSL::Crypto)
-    else()
-        # LibreSSL
-        set(LIBRESSL_SKIP_INSTALL ON CACHE BOOL "")
-        set(OPENSSLDIR "/etc/ssl/")
-        add_subdirectory(libressl EXCLUDE_FROM_ALL)
-        target_include_directories(ssl INTERFACE ./libressl/include)
-        target_compile_definitions(ssl PRIVATE -DHAVE_INET_NTOP)
-        get_directory_property(OPENSSL_LIBRARIES
-            DIRECTORY libressl
-            DEFINITION OPENSSL_LIBS)
-    endif()
-    # JSON
-    add_library(json-headers INTERFACE)
-    target_include_directories(json-headers INTERFACE ./json)
-
-    if(ANDROID)
-        add_subdirectory(android-ifaddrs)
-    endif()
-
-    # httplib
-    add_library(httplib INTERFACE)
-    target_include_directories(httplib INTERFACE ./httplib)
-    target_compile_options(httplib INTERFACE -DCPPHTTPLIB_OPENSSL_SUPPORT)
-    target_link_libraries(httplib INTERFACE ${OPENSSL_LIBRARIES})
-
-    # cpp-jwt
-    SET(CPP_JWT_USE_VENDORED_NLOHMANN_JSON ON CACHE BOOL "Use included json-hpp")
-    add_library(cpp-jwt INTERFACE)
-    target_include_directories(cpp-jwt INTERFACE ./cpp-jwt/include)
-    target_compile_definitions(cpp-jwt INTERFACE CPP_JWT_USE_VENDORED_NLOHMANN_JSON)
-endif()
-
-# lodepng
-add_subdirectory(lodepng)
-
-# (xperia64): Only use libyuv on Android b/c of build issues on Windows and mandatory JPEG
-if(ANDROID)
-    # libyuv
-    add_subdirectory(libyuv)
-    target_include_directories(yuv INTERFACE ./libyuv/include)
-endif()