Split UnwrappedLineFormatter into individual components.

Goals: Structure code better and make components easier to use for
future features (e.g. column layout for long braced initializers).

No functional changes intended.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188543 91177308-0d34-0410-b5e6-96231b3b80d8