Rename `SetResultIsInternal` and `GetResultIsInternal` to `SetSuppressPersistentResult`
and `GetSuppressPersistentResult` respectively. Also rename `m_result_is_internal`.
This matches the naming in the SB API.
A separate change calls `SetSuppressPersistentResult`, where the name
`SetResultIsInternal` doesn't quite fit.
Differential Revision: https://reviews.llvm.org/D144042