Color contrast survey updates

[tombrunet]

Changes include:

• Removes the restriction of applicability to widgets. Maintains exclusion for disabled widgets.
  • This caused inapplicable examples to now passed using default browser colors
  • Created two failing testcases using buttons with CSS colors
• Clarifies how to compute the maximum possible contrast between two sets of colors.
• Add shadow to minimum contrast, similar to how it was applied to enhanced contrast

Notes:

• Please review issues (Should colour contrast rules (afw4f7, 09o5cg) test content of tables? #1763 and The text contrast rules should not exclude text in active user interface components #1791) to ensure that the widget changes match what was intended.
• @WilcoFiers @kengdoj please review drop shadow on minimum to ensure this is what was intended. I maintained the lower text contrast but added the same drop shadow as the enhanced version.

Closes issue(s):

• closes Should colour contrast rules (afw4f7, 09o5cg) test content of tables? #1763
• closes The text contrast rules should not exclude text in active user interface components #1791

Need for Call for Review:
This will require a 2 weeks Call for Review << new rule, or substantial changes affecting a large number of test cases, if in doubt, use this.

---

Pull Request Etiquette

When creating PR:

• Make sure you're requesting to pull a branch (right side) to the develop branch (left side).
• Make sure you do not remove the "How to Review and Approve" section in your pull request description

After creating PR:

• Add yourself (and co-authors) as "Assignees" for PR.
• [ x Add label to indicate if it's a Rule, Definition or Chore.
• Link the PR to any issue it solves. This will be done automatically by referencing the issue at the top of this comment in the indicated place.
• Optionally request feedback from anyone in particular by assigning them as "Reviewers".

When merging a PR:

• Close any issue that the PR resolves. This will happen automatically upon merging if the PR was correctly linked to the issue, e.g. by referencing the issue at the top of this comment.

How to Review And Approve

• Go to the “Files changed” tab
• Here you will have the option to leave comments on different lines.
• Once the review is completed, find the “Review changes” button in the top right, select “Approve” (if you are really confident in the rule) or "Request changes" and click “Submit review”.
• Make sure to also review the proposed Call for Review period. In case of disagreement, the longer period wins.

[WilcoFiers]

No wait, the other one :-) I'd like some examples.

Updated, check again

[WilcoFiers]

Minor changes

Changes made

[Jym77]

Editorial comments. Nothing is blocking.

I think we could also have test cases with other widgets than button.