lupdate clang-parser: get the list of headers with new preprocessor function for llvm version >= 14

Comments of type /* TRANSLATOR */ are not associated to a translation call.

To retrieve them, the raw comments have to be parsed. For llvm version 10 and up, the raw comments can only be retrieved for a given file.

To retrieve those comments for headers, the headers have to be listed. Currently the headers are listed during preprocessing via the InclusionDirective function. The list of headers is then saved, and passed to the AST visiting tool.

For llvm version 14, this should not be needed anymore since the preprocessor has a new functionality (getIncludedFiles()) to call the list of included files.

This implies passing the preprocessor to the AST Visitor, at construction time.