[LLDB] Add SBInstruction::GetControlFlowKind()

D128477 adds the control flow kind for `Instruction` and displays this
in the `thread trace dump instruction -k` command.

This diff exposes the control flow kind via the new
`SBInstruction::GetControlFlowKind` method.

I've expanded `TestDisassembleRawData` to test this method, but please
let me know if there are any other unittests that should also be updated.

Test Plan:
`./bin/lldb-dotest -p TestDisassembleRawData`

Differential Revision: https://reviews.llvm.org/D131005