fix(table_headers_exists): fix issues related to the case of multiple headers for both rows and columns

[shunguoy]

fix(table_headers_exists): fix issues related to the case of multiple headers for both rows and columns

Please review more info: https://github.com/IBMa/equal-access/wiki/Release-notes -->

Rule bug: table_headers_exists

This PR is related to the following issue(s):

#1472

Testing reference:

1. test/v2/checker/accessibility/rules/table_headers_exists_ruleunit/table_multiple_headers.htm
2. test/v2/checker/accessibility/rules/table_headers_exists_ruleunit/table_headers_row_association.htm
   Notice that the violation "Table has no headers identified" was fixed.

I have conducted the following for this PR:

• I validated this code in Chrome and FF
• I validated this fix in my local env
• I provided details for testing
• This PR has been reviewed and is ready for test
• I understand that the title of this PR will be used for the next release notes.

[ErickRenteria]

Undet test