Twenty Fifteen - update aria attributes on primary menu

[bschneidewind]

On the 2015 theme, when a child menu item is the currently active page the menu will be expanded by default - however the aria-expanded attribute remains false and attribute toggles the incorrect value when opened/closed.

The aria-controls attribute is currently not present.

The PR resolves both these items.

Trac ticket: https://core.trac.wordpress.org/ticket/62936

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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Props bschneidewind, joedolson.

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[github-actions]

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[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 59916
GitHub commit: ad039b2

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.