Incorrect highlighting for C++ special identifiers

[aladram]

C++ identifiers with special meaning (final, override, import and module). are incorrectly highlighted out-of-context. These keywords should be considered as regular identifiers when used out of their special meaning context (c.f. C++20 standard, section 5.10, paragraph 2).

Reproduction:

int final, override, import, module;

Actual: these variables names are incorrectly highlighted as keywords. Expected: no specific highlighting.

Refers to vim/vim#8745.