[llvm-profgen] Use context-sensitive byte size cost for preinliner decisions by default

Turn on `use-context-cost-for-preinliner` to use context-sensitive byte size cost for preinliner decisions by default.

This is a more accurate proxy of inline cost than profile size. We tested on our large workload that it delivers measureable CPU improvement.

Differential Revision: https://reviews.llvm.org/D109893