[@mantine/core] Checkbox: Add aria-describedby support for error and description (#8340)

[hlongc]

What

Fixes #8340

Checkbox error messages are now accessible to screen readers like VoiceOver. Previously, the error and description text were not announced when focusing on the checkbox input.

Changes

• Added aria-describedby attribute to checkbox input element
• The attribute references the IDs of description and error elements
• Updated InlineInput to accept optional descriptionId and errorId props
• Added test cases to verify the accessibility improvements

How it works

When a Checkbox has an error or description:

1. Generate unique IDs for description/error elements
2. Set these IDs on the actual description/error elements
3. Link the checkbox input to these elements via aria-describedby

This ensures screen readers properly announce the description and error messages when users focus on the checkbox.

Testing

All tests pass (54/54):

• ✅ aria-describedby set correctly when only error is present
• ✅ aria-describedby set correctly when only description is present
• ✅ aria-describedby references both IDs when both are present
• ✅ No aria-describedby when neither is present

Tested with Mac VoiceOver - error messages are now properly announced. 🎉