Merge branch 'js/userdiff-cpp'

Userdiff patterns for the C++ language has been updated.

* js/userdiff-cpp:
  userdiff-cpp: back out the digit-separators in numbers
  userdiff-cpp: learn the C++ spaceship operator
  userdiff-cpp: permit the digit-separating single-quote in numbers
  userdiff-cpp: prepare test cases with yet unsupported features
  userdiff-cpp: tighten word regex
  t4034: add tests showing problematic cpp tokenizations
  t4034/cpp: actually test that operator tokens are not split