Xlsx Reader Use Dynamic Arrays if Spreadsheet Did So

[oleibman]

By default, when an Xlsx spreadsheet is read, its calculation engine is set to RETURN_ARRAY_AS_VALUE for array formulas. The user does have the option to change this. However, the presence of certain metadata in the file indicates that it was saved as if RETURN_ARRAY_AS_ARRAY was in use. This PR tests for the metadata, and, if present, sets ...ARRAY rather than ...VALUE. This eliminates the need for any extra action on the user's part.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary