fix: Add aromatic aluminium token

[iwyoo]

Reference Issue

Fixes #3697

What does this implement/fix? Explain your changes.

By Huckel's rule, rdkit sometimes converts [Al+] to [al+], but current rdkit cannot read [al because there is no lex rule for it.

Any other comments?

[greglandrum]

@iwyoo , thanks for the contribution.
I think a better fix for this would be to avoid generating the aromatic token for Al in the first place.
So the modification would be to SmilesWrite.cpp, around line 231, to make sure that it only changes the first letter in the atomic symbol to be aromatic if the atomic number is 5, 6, 7, 8, 14, 15, 16, 33, 34, or 52

Otherwise we'll constantly have to add new aromatic tokens, and that cause us to move further and and further away from what the old daylight documentation says: section 3.4.2 here https://daylight.com/dayhtml/doc/theory/theory.smiles.html

[iwyoo]

@greglandrum Thanks! I just deleted the previous changes and applied the correct revision to SmilesWrite.cpp you mentioned.

[greglandrum]

Thanks for updating the PR.

The one piece which is missing for this to be added is a test to demonstrate that the changes work (and make sure that if the behavior changes in the future we will detect it).

Please add the new test(s) to v2catch_tests.cpp in the SmilesParse directory; you can use the tests that are there or in catch_tests.cpp as a template for what the tests should look like.

Let me know if you have any questions.