First step towards correctly formatting lambdas.

Implements parsing of lambdas in the UnwrappedLineParser.
This introduces the correct line breaks; the formatting of
lambda captures are still incorrect, and the braces are also
still formatted as if they were braced init lists instead of
blocks.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189818 91177308-0d34-0410-b5e6-96231b3b80d8