fix(Table): Keyboard Navigation Support

[elephantcatdog]

Fixed sorting, filtering, and anchor navigation issues in the table.

Sorting:

• Added tabIndex and onKeyDown to the div that contains the sort icon button

Filtering

• Filtering is fixed by no longer making the button visibility: hidden when not hovered on. Instead of using visibility to control the look of the button, I changed it to use opacity. This is done in the CSS repo and more info can be found at that PR: https://github.com/iTwin/iTwinUI/pull/752

Anchors

• I added tabIndex and onKeyDown props to the anchors found in Table.stories.tsx. I also tried fiddling with the table's tabIndex={-1}, but that wasn't affecting this issue.
• One of the stories does not check if the key pressed is "Enter" (lines 1064-1068). I couldn't figure out how to do it and retain the functionality of the actions tab on Storybook.

Added tests for sorting and filtering

• The test for filtering does not work correctly, even though it passes, because it also passes when it's supposed to fail. I assume that userEvent.tab() is a 'better' tab than that made by using the keyboard? Because it's able to correctly tab through the filtering menu even when visibility: hidden.

Closes iTwin/iTwinUI-react#488

Checklist

• [x] Add meaningful unit tests for your component (verify that all lines are covered)
• [x] Verify that all existing tests pass
• ~[ ] Add component features demo in Storybook (different stories)~ not needed
• ~[ ] Approve test images for new stories~ not needed
• [x] Add screenshots of the key elements of the component

[elephantcatdog]

There are extraneous changes shown in this PR right now because the main branch hasn't been merged into itwinui-css-v1 (how to do?), and I initially made this branch off of main. If you want to review it, the relevant changes are in Table.tsx, Table.test.tsx, and Table.stories.tsx.

[elephantcatdog]

I checked if Buttons were accessible with the keyboard within a table and they are. The issue with Anchors in a table doesn't seem to be a table issue.

[elephantcatdog]

I played with the tests, trying to get it to work (fail) for the filter test, but couldn't. I dunno if it helps someone help me to leave it like this, but the alternative is to remove the filter test because it'll pass even if it should fail.

[elephantcatdog]

The problems with Anchor were further reaching than I thought I should go for this PR, so I made a new issue: https://github.com/iTwin/iTwinUI/issues/904

[elephantcatdog]

I removed the test for filtering navigation as I couldn't find a solution to make it fail/pass correctly.