Always break after multi-line string literals.

Otherwise, other parameters can be quite hidden.
Reformatted unittests/Format/FormatTest.cpp after this.

Before:
someFunction("Always break between multi-line"
             " string literals", and, other, parameters);

After:
someFunction("Always break between multi-line"
             " string literals",
             and, other, parameters);

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175436 91177308-0d34-0410-b5e6-96231b3b80d8