CI: Add nlohmann JSON, WebSocket++ and Asio on Linux

Those libraries will be kept in the Flatpak to allow plugins to use the
same versions of those headers-only libraries.

CI/flatpak/com.obsproject.Studio.json

@@ -409,6 +409,59 @@
         }
       ]
     },
+    {
+      "name": "nlohmann-json",
+      "buildsystem": "cmake-ninja",
+      "builddir": true,
+      "config-opts": [
+        "-DCMAKE_BUILD_TYPE=Release",
+        "-DJSON_BuildTests=OFF"
+      ],
+      "sources": [
+        {
+          "type": "git",
+          "url": "https://github.com/nlohmann/json.git",
+          "tag": "v3.11.2",
+          "commit": "bc889afb4c5bf1c0d8ee29ef35eaaf4c8bef8a5d"
+        }
+      ]
+    },
+    {
+      "name": "websocketpp",
+      "buildsystem": "cmake-ninja",
+      "builddir": true,
+      "config-opts": [
+        "-DCMAKE_BUILD_TYPE=Release",
+        "-DENABLE_CPP11=ON",
+        "-DBUILD_EXAMPLES=OFF",
+        "-DBUILD_TESTS=OFF"
+      ],
+      "sources": [
+        {
+          "type": "git",
+          "url": "https://github.com/zaphoyd/websocketpp.git",
+          "tag": "0.8.2",
+          "commit": "56123c87598f8b1dd471be83ca841ceae07f95ba"
+        }
+      ]
+    },
+    {
+      "name": "asio",
+      "buildsystem": "simple",
+      "build-commands": [
+        "mkdir -p /app/include",
+        "cp asio/include/asio.hpp /app/include/",
+        "cp -R asio/include/asio /app/include/"
+      ],
+      "sources": [
+        {
+          "type": "git",
+          "url": "https://github.com/chriskohlhoff/asio.git",
+          "tag": "asio-1-12-1",
+          "commit": "b73dc1d2c0ecb9452a87c26544d7f71e24342df6"
+        }
+      ]
+    },
     {
       "name": "cef",
       "buildsystem": "cmake-ninja",

CI/linux/01_install_dependencies.sh

@@ -95,7 +95,8 @@ install_dependencies() {
         "qt6-deps qt6-base-dev qt6-base-private-dev libqt6svg6-dev qt6-wayland"
         "cef ${LINUX_CEF_BUILD_VERSION:-${CI_LINUX_CEF_VERSION}}"
         "plugin-deps libasound2-dev libfdk-aac-dev libfontconfig-dev libfreetype6-dev libjack-jackd2-dev \
-         libpulse-dev libsndio-dev libspeexdsp-dev libudev-dev libv4l-dev libva-dev libvlc-dev libdrm-dev"
+         libpulse-dev libsndio-dev libspeexdsp-dev libudev-dev libv4l-dev libva-dev libvlc-dev libdrm-dev \
+         nlohmann-json3-dev libwebsocketpp-dev libasio-dev"
     )
 
     sudo apt-get -qq update