[EuiCheckbox][EuiRadio] Fix checkboxes/radios without labels not being clickable

[cee-chen]

Summary

closes #5145 (NB: This bug only exists in 37.6.1, and should be fixed in 37.6.2)

#5130 updated the euiScreenReaderOnly mixin (which EuiCheckbox and EuiRadio both use) to include clip(0 0 0 0) CSS (to prevent scrolling issues caused by absolute positioning). Per the QA section of that PR, I tested the change against the normal checkbox/radio examples in our docs, but did not test them against checkbox/radios with no labels (which I hadn't realized functioned slightly differently than their counterparts with labels).

Checkboxes and radios without labels actually do not want the standard euiScreenReaderOnly behavior. The visually hidden input actually overlays the visually displayed element with a set height/width, unlike SR behavior which moves the hidden element totally offscreen.

As such, I decided the cleanest solution would be to only apply the euiScreenReaderOnly CSS to checkboxes/radios with labels (using :not()), thus negating the need for checkbox/radios to override any parts euiScreenReaderOnly CSS.

Before

After

Checkboxes/radios with labels remain the same:

QA

• Go to https://eui.elastic.co/pr_5149/#/tabular-content/tables#adding-selection-to-a-table and confirm the table row selection is now clickable
• (Regression testing) Go to https://eui.elastic.co/pr_5149/#/forms/form-controls#checkbox and confirm that checkbox and radio inputs still look and function correctly/as before
• Open the playgrounds for the EuiCheckbox and EuiRadio elements, and clear the Label input. Confirm the inputs are still interactable (NB: the checkbox playground doesn't change state, but the radio playground does)

Checklist

- [ ] Check against all themes for compatibility in both light and dark modes
- [ ] Checked in mobile

• Checked in Chrome, Safari, Edge, and Firefox

- [ ] Props have proper autodocs and playground toggles
- [ ] Added documentation
- [ ] Checked Code Sandbox works for the any docs examples
- [ ] Added or updated jest tests
- [ ] Checked for breaking changes and labeled appropriately

• Checked for accessibility including keyboard-only and screenreader modes
• A changelog entry exists and is marked appropriately

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5149/

[thompsongl]

Why this change?

[cee-chen]

If you check out the "Before" screenshot, left: 0 was presumably added to override left: -10000px being set by euiScreenReaderOnly CSS. If you remove the CSS from being loaded at all on this input, there's no need to set left: 0 - position absolute will typically float the element where it would originally have been placed

[thompsongl]

LGTM
Also tested the other "checkable" components that use the mixin (EuiKeyPadMenuItem, EuiResizableCollapseButton) and saw no regression

[cee-chen]

@thompsongl Apologies for any wasted time on your part, @cchaos pinged me to let me know she'd rather revert #5130 for the next patch release. I'm going to close this PR, open a reversion PR, and then open a PR with #5130 plus this fix with a target release of the next breaking major (38.x).

CC @chandlerprall as a heads up