[lldb/Fuzzer] Add command interpreter fuzzer for LLDB

This adds a command interpreter fuzzer to LLDB's fuzzing library.
The input data from the fuzzer is used as input for the command
interpreter.
Input data for the fuzzer is guided by a dictionary of keywords used in
LLDB, such as "breakpoint", "target" and others.

Differential revision: https://reviews.llvm.org/D128292