Refactor datastructure used in clang-format.

Main difference, add an AnnotatedLine class to hold information about a
line while formatting. At the same time degrade the UnwrappedLine class
to a class solely used for communicating between the UnwrappedLineParser
and the Formatter.

No functional changes intended.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172403 91177308-0d34-0410-b5e6-96231b3b80d8