Update Toast to use the central live region for announcements

[maribethb]

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Problem

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Request

Blockly has support for showing important but non-essential UI affordances toasts which are generally important enough to be read out to the user (with customizable assertiveness). These currently manage their own status role property. However, the central Toast utility will need to be updated to use announceDynamicAriaState() instead of managing its own internal live region. It will need to pass along the status role and assertiveness to use.

Alternatives considered

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Additional context

Depends on #9632