Improve the performance of jModulesInfo in lldb-server

Previously it parsed /proc/<pid>/maps for every module separately
resulting in a very slow response time. This CL add some caching and
optimizes the implementation to improve the code from O(n*m) to O(n+m)
where n is the number of modules requested and m is the number of
files mapped into memory.

Differential revision: https://reviews.llvm.org/D28233

llvm-svn: 290895