Add Fix*Address methods to Process, call into ABI

We need to clear non-addressable bits from addresses across
the lldb sources.  Currently these need to use an ABI method
to clear those bits from addresses, which you do by taking a
Process, getting the current ABI, then calling the method.

Simplify this by providing methods in Process which call into
the ABI methods themselves.

Differential Revision: https://reviews.llvm.org/D152863