Add Discord Rich Presence Support (#3883)

* Initial Discord RPC support

Build with Discord Presence ON

Fix RPC detection

Fix Time elapsed on pause; will now continue to count.

* Fix CI builds with compile flag

Addressed reviews

Fix silly mistakes

Fix 'Not in-game' display

class instead of namespace

Fix

Revamped

remove redundant code

Using Pimpl pattern

* Implement Null class

* Fix config updation

* Addressed All Reviews

* externals/discord-rpc : Updated to latest commit

externals/CMakeLists.txt

@@ -62,6 +62,18 @@ endif()
 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)
+    target_include_directories(discord-rpc INTERFACE ./discord-rpc/include)
+endif()
+
 if (ENABLE_WEB_SERVICE)
     # LibreSSL
     set(LIBRESSL_SKIP_INSTALL ON CACHE BOOL "")
@@ -80,9 +92,3 @@ if (ENABLE_WEB_SERVICE)
     add_library(json-headers INTERFACE)
     target_include_directories(json-headers INTERFACE ./json)
 endif()
-
-# Cubeb
-if(ENABLE_CUBEB)
-    set(BUILD_TESTS OFF CACHE BOOL "")
-    add_subdirectory(cubeb EXCLUDE_FROM_ALL)
-endif()