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.

Tests/AK/TestQueue.cpp

@@ -52,7 +52,7 @@ TEST_CASE(order)
     }
 
     for (int i = 0; i < 10000; ++i) {
-        EXPECT_EQ(strings.dequeue().to_int().value(), i);
+        EXPECT_EQ(strings.dequeue().to_number<int>().value(), i);
     }
 
     EXPECT(strings.is_empty());