Merge topic 'refactor-lexer'

e947e7b6e2 cmListFileCache: use cmStrCat instead of string stream
55a4a585fa cmListFileParser: use unique_ptr to own cmListFileLexer instance
63f8134744 cmListFileCache: convert cmListFileParser from struct to class
1bf4900df7 cmListFileCache: avoid redundant operator<< calls
459c01d520 cmListFileCache: move cmListFileParser into an anonymous namespace

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Merge-request: !9680