Fix when placing flextable footnote to multiple columns and rows

[ddsjoberg]

What changes are proposed in this pull request?

• Bug fix when placing a footnote for flextable tables on multiple columns and rows. (Bug Report: as_flex_table doesn't pass multi-column/row footnote coordinates correctly #2062)

If there is an GitHub issue associated with this pull request, please provide link.
closes #2062

@Melkiades before fully reviewing this PR, can you add a test or two more for different types of footnote placement to ensure they are correctly placed when there is one column and multiple rows, multiple columns and one row, and one mixed-type when the column/rows are contiguous? Thank you!

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[Melkiades]

@ddsjoberg added a test, let me know if it was what you were looking for. Only place where I cannot add a footnote is the stubhead so far

[Melkiades]

Thanks Daniel for the fix. If It is what you need feel free to merge. From my side, I could not break it :D

[ddsjoberg]

Thanks @Melkiades ! Can you take a look into the failing CI/CD?