Add --primary_abi_only to command_sheet

- Support comparing two cts-on-gsi reports even if the bitness of the
  primary ABIs is different.
- Move _ParseSummary from command_sheet to result_utils.

Bug: 79905934
Test: sheet --src= --ref= --dest= --primary_abi_only
Change-Id: Ifd47459556042a62c05ae5a0d20be9507fa2d562