Get Style for Row or Column

[oleibman]

This is the second recent occasion where style for whole row or column is behaving unexpectedly (see issue #4285). For the earlier issue, a documentation update was made to show the preferred method of styling. Setting styles for row(s) or column(s) in that way will work just fine, however retrieving the style doesn't yield the expected result. Although that problem can be overcome with existing code, simpler methods are needed, and this PR adds methods getRowStyle and getColumnStyle to Worksheet. I will continue to investigate why this problem and the one from 4285 have unexpected results.

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

Why this change is needed?

Provide an explanation of why this change is needed, with links to any Issues (if appropriate).
If this is a bugfix or a new feature, and there are no existing Issues, then please also create an issue that will make it easier to track progress with this PR.