feat: add keyboard focus styles

[r3pwn]

Description

The Admin site does not currently have any kind of keyboard focus styles, meaning that tabbing through elements on a page may prove to be difficult for some users.

This PR aims to resolve that by adding keyboard focus styles for a majority of the components, as well as provides a couple incredibly minor bugfixes related to tab-based navigation:

• prevents tabbing to a disabled Paginator/ClickableArrow by setting the disabled HTML attribute on it
• prevents tabbing to the invisible textarea that CopyToClipboard uses internally

For users that do not use a keyboard to navigate the site, there is no perceivable change, as this approach utilizes the :focus-visible CSS pseudo-selector.

While it is more of a minor accessibility fix, this change relates to #1232

• I have read and understand the CONTRIBUTING.md document in this repository

Type of change

• 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 not work as expected)
• This change requires a documentation update

[AlessioGr]

Thank you for your PR! While reviewing it, I've noticed that the Dashboard Card outlines did not work. The issue was that the postcss-preset-env dependency was turning the &:focus:not(:focus-visible) into :focus:not(.focus-visible).

I went ahead and updated the postcss-preset-env dependency, which fixed this. Will continue my review of this PR to get this merged asap!

[AlessioGr]

LGTM!

Before:

Screenshot.2023-07-24.at.16.41.56.mp4

After:

Screenshot.2023-07-24.at.16.43.45.mp4