TimePicker: use ToggleGroupControl for AM/PM toggle

[ciampo]

What?

Closes #61163

Use ToggleGroupControl in TimePicker instead of button

Why?

For better semantics and screen readers support (ToggleGroupControl implements radio semantics)

How?

• swap out ButtonGroup and Button for ToggleGroupControl and ToggleGroupControlOption;
• use the onChange callback instead of onClick handlers
• update tests to reflect the new semantics

Testing Instructions

• Test component both in Storybook and in the editor (for example, by setting a future publishing date for a post)
• Make sure that the AM/PM toggle is shown (that happens if the is12Hour prop is true)
• Make sure that the datetime is updated correctly as the toggle is interacted with (including first load)
• Make sure that the new version of the toggle implements radio semantics correctly and is accessible for screen reader users

Screenshots or screencast

Before (trunk)	After (this PR)

[github-actions]

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Co-authored-by: ciampo <[email protected]>
Co-authored-by: mirka <[email protected]>
Co-authored-by: jasmussen <[email protected]>
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[mirka]

Looks good 🚀

[mirka]

I think we can frame this as a full-on bug fix since it was previously inaccessible.

[mirka]

Do you think we can remove this className now? I can't really imagine a style override that was applied on the previous implementation that would still work as intended in the new implementation 😂

[ciampo]

Sounds good

[ciampo]

The components-datetime__time-field is actually used in more places throughout the component, but for the scope of this PR I've only removed it from ToggleGroupControl.

If you think it makes sense, I can open a follow-up removing those other instances too.

[jeffpaul]

@MadGanGithub mind sharing your WordPress.org username so I can ensure its included in the 6.7 credits listing?