[LLDB] Added syntax highlighting support

[LLDB] Added syntax highlighting support

Summary:
This patch adds syntax highlighting support to LLDB. When enabled (and lldb is allowed
to use colors), printed source code is annotated with the ANSI color escape sequences.

So far we have only one highlighter which is based on Clang and is responsible for all
languages that are supported by Clang. It essentially just runs the raw lexer over the input
and then surrounds the specific tokens with the configured escape sequences.

Reviewers: zturner, davide

Reviewed By: davide

Subscribers: labath, teemperor, llvm-commits, mgorny, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D49334

llvm-svn: 338662