[BOLT] Deduplicate equal offsets in BAT (#76905)

Encode BRANCHENTRY bits as bitmask for deduplicated entries.

Reduces BAT section size:
- large binary: to 11834216 bytes (0.31x original),
- medium binary: to 1565584 bytes (0.26x original),
- small binary: to 336 bytes (0.23x original).

Test Plan: Updated bolt/test/X86/bolt-address-translation.test