AK: Add FloatingPoint.h

This is a set of functions that allow you to convert between arbitrary
IEEE 754 floating point types, as long as they can be represented
within 64 bits. Conversion methods between floats and doubles are
provided, as well as a generic `float_to_float()`.

Example usage:

  #include <AK/FloatingPoint.h>

  double val = 1.234;
  auto weird_f16 =
      convert_from_native_double<FloatingPointBits<0, 6, 10>>(val);

Signed and unsigned floats are supported, and both NaN and +/-Inf are
handled correctly. Values that do not fit in the target floating point
type are clamped.

Tests/AK/CMakeLists.txt

@@ -26,6 +26,7 @@ set(AK_TEST_SOURCES
     TestEnumBits.cpp
     TestFind.cpp
     TestFixedArray.cpp
+    TestFloatingPoint.cpp
     TestFormat.cpp
     TestGenericLexer.cpp
     TestHashFunctions.cpp