Deduplicate register masks

Data is commonly shared between different stack maps. The register
masks are stored after the stack masks.

Oat size for a large app:
96722288 -> 94485872 (-2.31%)

Average oat size reduction according to golem -3.193%.

Bug: 34621054

Test: test-art-host

Change-Id: I5eacf668992e866d11ddba0c01675038a16cdfb4