Stack maps: Refactor constructors.

Create dedicated static methods instead of passing flags.
This creates dedicated methods for the purpose and merges
constructor and decoding into single optimized method.

This speeds up CodeInfo by 10%, and maps startup by 0.1%.

Test: ./art/test.py -b --host
Change-Id: Ic7d43e22bca0be9fb13bc2c7544ebfdf46798cfe
8 files changed