MCDwarf: Rename MCDwarfFileTable to MCDwarfLineTable

This type now represents all the data for the DWARF line table:
directory names, file names, and the line table proper.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203858 91177308-0d34-0410-b5e6-96231b3b80d8