Enable lldm-mi commands -stack-list-locals -stack-list-variables and...

Enable lldm-mi commands -stack-list-locals -stack-list-variables and -var-create to work only with variables in scope

Patch by ayuckhulk

Reviewers: abidh, lldb-commits, ki.stfu

Reviewed By: ki.stfu

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D31073

llvm-svn: 299417