AK: Add Formatter<FixedPoint<...>> without floating point

Rather than casting the FixedPoint to double, format the FixedPoint
directly. This avoids using floating point instruction, which in
turn enables this to be used even in the kernel.

AK/FixedPoint.h

@@ -315,21 +315,6 @@ private:
     Underlying m_value;
 };
 
-template<size_t precision, Integral Underlying>
-struct Formatter<FixedPoint<precision, Underlying>> : StandardFormatter {
-    Formatter() = default;
-    explicit Formatter(StandardFormatter formatter)
-        : StandardFormatter(formatter)
-    {
-    }
-
-    ErrorOr<void> format(FormatBuilder& builder, FixedPoint<precision, Underlying> value)
-    {
-        Formatter<double> formatter { *this };
-        return formatter.format(builder, (double)value);
-    }
-};
-
 }
 
 using AK::FixedPoint;