[clang-tidy] Fix bug 34747, streaming operators and hicpp-signed-bitwise

The bug happened with stream operations, that were not recognized in all cases.
Even there were already existing test for streaming classes, they did not catch this bug.
Adding the isolated example to the existing tests did not trigger the bug.
Therefore i created a new isolated file that did expose the bug indeed.

Differential: https://reviews.llvm.org/D38399
reviewed by aaron.ballman

llvm-svn: 314808