Add a flag to QDoc that allows the inspection of the intermediate results for parsing

When QDoc parses a file for QDoc's block comments, it builds an intermediate representation of Atom types that represent the parsed content.

This representation is later processed to generate the required output.

It would be useful to be able to inspect this structure when trying to debug the parsing of a specific use-case or just to build a more general understanding of how QDoc sees things at the parsing level.

To allow for this, it is proposed to introduce a new command-line flag, --atoms-dump, that, when passed together with --debug, would show a human-readable version of the parsed atoms in the debug output.

The feature is intended to be inspired by Clang's ast-dump and aims to provide the same benefit to the debugging and discoverability capabilities of QDoc.

It is further suggested to consider, after the addition of this feature, the implementation of a testing structure, similar to tst_generatedOutput, that ensure the compatibility of the relevant intermediate representation between changes.