[SampleProfile] Use CallBase in function arguments and data structures to...

[SampleProfile] Use CallBase in function arguments and data structures to reduce the number of explicit casts. NFCI

Removing CallSite left us with a bunch of explicit casts from
Instruction to CallBase. This moves the casts earlier so that
function arguments and data structure types are CallBase so
we don't have to cast when we use them.

Differential Revision: https://reviews.llvm.org/D78246