Everywhere: Use to_number<T> instead of to_{int,uint,float,double}

In a bunch of cases, this actually ends up simplifying the code as
to_number will handle something such as:

```
Optional<I> opt;
if constexpr (IsSigned<I>)
    opt = view.to_int<I>();
else
    opt = view.to_uint<I>();
```

For us.

The main goal here however is to have a single generic number conversion
API between all of the String classes.

Userland/Utilities/lsof.cpp

@@ -136,7 +136,7 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     }
     {
         // try convert UID to int
-        auto arg = ByteString(arg_uid).to_int();
+        auto arg = ByteString(arg_uid).to_number<int>();
         if (arg.has_value())
             arg_uid_int = arg.value();
     }