Support table refs

[IvanHristov98]

Add support for table referencing (aka structured references)

Description

After experimenting I noticed that table references aren't supported.

Docs used for reference during implementation:

• https://support.microsoft.com/en-us/office/using-structured-references-with-excel-tables-f5ed2452-2337-4f71-bed3-c8ae6d2b276e
• https://support.google.com/docs/answer/15637642?hl=en

Related Issue

#2062

Motivation and Context

It allows table referencing when calculating cell formulas.

How Has This Been Tested

I tested it with unit tests. TODO (will test with actual files)

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document. (couldn't find such a document)
• I have added tests to cover my changes.
• All new and existing tests passed.

[IvanHristov98]

I have missed the case where a table is in a different sheet. Will cover it.

It is a bit trickier when initially reading the excel file. Hence I'll finish what's left in the beginning of the next week.

Hence the PR is currently in a draft phase.

[IvanHristov98]

Hi @xuri, I think that it is ready for a review. Implementing the cross sheet table reference was tricky.

TLDR I had to read a handful of metadata files until I could create the mapping:

1. Read from xl/workbook.xml to get the sheets metadata.
2. Read from xl/_rels/workbook.xml.rels to get the respective sheet metadata files of the sheets. It turns out that just sheet numeric ID isn't reliable. Hence I had to additionally parse this file.
3. Read from xl/worksheets/_rels/sheetX.xml.rels files to find the referenced tables.
4. Read from xl/tables/tableX.xml files to find the related table names.

The parsed files are metadata files, that should be small. Thus I think/hope that reading them shouldn't harm the performance of the library when calling OpenFile. 🤞

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I think that the PR is now ready for a review.

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Just one additional question. I tested table referencing of files opened with OpenFile manually. I tried adding a test xlsx file to the repo but there is a .gitignore that prevents me from adding it to the test directory.

Any advices here? I'd like to bring a more complete unit test coverage.

[xuri]

Thanks for your PR. I have been busy recently, will review for this as soon as possible.