Add support for int-to-float & int-to-double in optimizing.

- Add support for the int-to-float and int-to-double Dex
  instructions in the optimizing compiler.
- Generate x86, x86-64 and ARM (but not ARM64) code for
  byte to float, short to float, int to float, char to
  float, byte to double, short to double, int to double and
  char to double HTypeConversion nodes.
- Add related tests to test/422-type-conversion.

Change-Id: I963f9d0184a5d3721af2d8f593f133d5af7aa6a3