Add support for long-to-int in the optimizing compiler.

- Add support for the long-to-int Dex instruction in the
  optimizing compiler.
- Generate x86, x86-64 and ARM (but not ARM64) code for
  long-to-int HTypeConversion nodes.
- Add related tests to test/422-type-conversion.
- Also fix comments in test/415-optimizing-arith-neg and
  in test/416-optimizing-arith-not.

Change-Id: I3084af30f2a495d178362ae1154dc7ceb7bf3a58