Imprrove table-has-headers check to handle more complex table markups

[pattonwebz]

Update the table-has-header check to deal with the TODO comment. The TODO should be fully tackled and removed with the changes.

accessibility-checker/src/pageScanner/checks/table-has-headers.js

Line 8 in e073408

// TODO: Improve logic to account for colspan, rowspan, and complex ARIA header relationships

A previous attempt was made in a different PR but reverted so it could be tackled in a dedicated PR so it can be better tested and decided on. You may want to take the same approach or a different one.

Commits to reference:
9c49dfa - Enhanced table-has-headers.js logic with ARIA support, colspan/rowspan handling
c4ab723 - Comprehensive test cases (16 additional tests)