DngCreator: Improve black level support; avoid large stack allocation

 - Switch the BlackLevel entry to be RATIONAL
 - Switch to heap allocation instead of stack allocation for lens
   shading map construction
 - Add orientation enums for convenience

Bug: 25862995
Bug: 27073274
Change-Id: I7031a33c4797dc8b2c8030d26b749066e03bff9e
2 files changed