Introduce lldb-framework CMake target and centralize its logic

Summary:
In this patch I aim to do the following:

1) Create an lldb-framework target that acts as the target that handles generating LLDB.framework. Previously, liblldb acted as the target for generating the framework in addition to generating the actual lldb library. This made the target feel overloaded.
2) Centralize framework generation as much as it makes sense to do so.
3) Create a target lldb-suite, which depends on every tool and library that makes liblldb fully functional. One result of having this target is it makes tracking dependencies much clearer.

Differential Revision: https://reviews.llvm.org/D48060

llvm-svn: 334968