Note [certainlyWillInline: INLINABLE]

certainlyWillInline /must/ return Nothing for a large INLINABLE thing,
even though we have a stable inlining, so that strictness w/w takes
place.  It makes a big difference to efficiency, and the w/w pass knows
how to transfer the INLINABLE info to the worker; see WorkWrap
Note [Worker/wrapper for INLINABLE functions]