[REG 12.0.2 -> 13.0] "Switch Between Function Declaration/Definition" does not work

1. Open cplusplus-tools manual test.
   It's in tests/manual/cplusplus-tools/cplusplus-tools.pro of Creator's source repository.
2. Open file dummy.cpp from that project.
3. Right-click on the line

   Dummy::Dummy(int)
   

   and select "Switch Between Function Declaration/Definition" from the context menu.
   Nothing happens.

Instead, Creator should open the file dummy.h and place the cursor in the line

Dummy(int a);

In Creator 12.0.2, this works correctly.

Found and tested by Squish test tst_basic_cpp_support.