[clang][dataflow] Unify `TransferOptions` and `DataflowAnalysisContext::Options`.

Merges `TransferOptions` into the newly-introduced
`DataflowAnalysisContext::Options` and removes explicit parameter for
`TransferOptions`, relying instead on the common options carried by the analysis
context. Given that there was no intent to allow different options between calls
to `transfer`, a common value for the options is preferable.

Differential Revision: https://reviews.llvm.org/D140703