[lldb] [test/lldb-vscode] Use realpath to match vscode behavior

Compare the directory paths returned by lldb-vscode against realpaths
rather than apparent paths.  This matches lldb-vscode behavior
and therefore fixes test failures when one of the parent directories
of the source tree is a symlink.

Differential Revision: https://reviews.llvm.org/D65432

llvm-svn: 367291