Evil159/footer support rebased

[bryankeller]

Details

This PR is a rebased version of #23. I went ahead and incorporated all of the feedback that I would have asked you to implement @evil159 in the last commit 433d0bc

Some notable changes I made:

• Simplified the footer layout logic in SectionModel. I want to avoid introducing additional flags and state. The addition of a new return-early case in the core layout function also made me nervous. The new code is less efficient, but more straightforward. I plan to refactor this function anyways so that recompute / invalidation is more explicit.
• Fixed tests (the original footer layout logic had a bug, and so the tests were buggy as well. See bf47285#diff-187bbc570783ead7c85afd619305a795R562 - how could a footer have 0 width?)
• Separated MagazineLayoutSupplementaryViewVisibilityMode into a MagazineLayoutHeaderVisibilityMode and MagazineLayoutFooterVisibilityMode. The reasoning for this is to ensure that this does not introduce a breaking API change.
• Minor indentation updates
• Minor naming updates
• Minor file organization updates

Related Issue

#18

Motivation and Context

How Has This Been Tested

Ran automated tests.

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.
• I have added tests to cover my changes.

[evil159]

Thank you so much for going through the trouble of fixing all the mishaps.

• Simplified the footer layout logic in SectionModel

Yes, it makes perfect sense to have it like that.

• how could a footer have 0 width?

😊 🤦‍♂️

[bryankeller]

It was the least I could do after not getting to the review for 2 months 😅 Thanks for your patience and for implementing this - this is an awesome feature to have, and gets us even closer to feature parody with flow layout!