...which was least buggy.

The bugs fixed by the changes we revert here (highlighting/completion
for code involving templates) were minor compared to ones we currently
have. Those bugs will be addressed by the clang code model anyway.

Relevant commits were collected via:

  $ cd ${QTC}/src/libs/cplusplus
  $ git log \
   --no-merges \
   --format=oneline \
   v3.4.2..HEAD \
   -- LookupContext.* ResolveExpression.* TypeResolver.* TypeOfExpression.* \
      ../../plugins/cpptools/cppcompletion_test.cpp

From this list the following were skipped due to irrelevance:

  88c5b47e # CppTools: Minor cleanup in completion tests
  e5255a1f # CppTools: Add a test for ObjC not replacing dot with arrow
  5b12c8d6 # CppTools: Support ObjC in member access operator tests
  9fef4fb9

 # CPlusPlus: Fix warnings about overriding visit(...) methods

There were only minor conflicts while reverting those.

This changes touches so many files because there were quite some
cleanups and renames after the 3.4.2 release.

Task-number: QTCREATORBUG-14889
Task-number: QTCREATORBUG-15211
Task-number: QTCREATORBUG-15213
Task-number: QTCREATORBUG-15257
Task-number: QTCREATORBUG-15264
Task-number: QTCREATORBUG-15291
Task-number: QTCREATORBUG-15329
Change-Id: I01f759f8f35ecb4228928a4f22086e279c1a5435
Reviewed-by: Marco Bubke <marco.bubke@theqtcompany.com>