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/profile.cpp

@@ -130,5 +130,5 @@ static Optional<pid_t> determine_pid_to_profile(StringView pid_argument, bool al
     }
 
     // pid_argument is guaranteed to have a value
-    return pid_argument.to_int();
+    return pid_argument.to_number<pid_t>();
 }