Support int-to-long conversions in the optimizing compiler.

- Add support for the int-to-float Dex instruction in the
  optimizing compiler.
- Add a HTypeConversion node type for control-flow graphs.
- Generate x86, x86-64 and ARM (but not ARM64) code for
  int-to-float HTypeConversion nodes.
- Add a 64-bit "Move doubleword to quadword with
  sign-extension" (MOVSXD) instruction to the x86-64
  assembler.
- Add related tests to test/422-type-conversion.

Change-Id: Ieb8ec5380f9c411857119c79aa8d0728fd10f780