fix(material/radio): button index not being read out by some screen readers

[crisbeto]

It looks like some screen reader / browser combinations (NVDA + Chrome in this case) won't read out the index of the radio button within the group correctly, if it's nested inside a label.

These changes fix the issue by moving the input outside of the label.

Fixes #23580.

[RadhikaGunisetty]

@crisbeto This PR needs a rebase.

[mmalerba]

Closing since this fix is for the legacy mat-radio which has been superseded by the MDC based one.

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