refactor: Make Args less of a singleton (#5041)

This means it's no longer a singleton, and its lifetime is bound to our application.
This felt like a good small experiment to see how its changes would look
if we did this.
As a shortcut, `getApp` that is already a mega singleton keeps a
reference to Args, this means places that are a bit more difficult to
inject into call `getApp()->getArgs()` just like other things are
accessed.

src/common/Args.cpp

@@ -1,4 +1,4 @@
-#include "Args.hpp"
+#include "common/Args.hpp"
 
 #include "common/QLogging.hpp"
 #include "debug/AssertInGuiThread.hpp"
@@ -248,18 +248,4 @@ void Args::applyCustomChannelLayout(const QString &argValue)
     }
 }
 
-static Args *instance = nullptr;
-
-void initArgs(const QApplication &app)
-{
-    instance = new Args(app);
-}
-
-const Args &getArgs()
-{
-    assert(instance);
-
-    return *instance;
-}
-
 }  // namespace chatterino

src/common/Args.hpp

@@ -30,6 +30,7 @@ namespace chatterino {
 class Args
 {
 public:
+    Args() = default;
     Args(const QApplication &app);
 
     bool printVersion{};
@@ -60,7 +61,4 @@ private:
     QStringList currentArguments_;
 };
 
-void initArgs(const QApplication &app);
-const Args &getArgs();
-
 }  // namespace chatterino