Bundled Themes: Accessibility additions to the site title link

[bschneidewind]

In bundled themes, adds the aria-current="page" (when applicable) and rel="home" to the site title link. The approach varies depending on how the theme is structured.
Updates:
TwentyTen
TwentyEleven
TwentyTwelve
TwentyThirteen
TwentyFourteen
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TwentySeventeen
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TwentyTwentyOne

Trac ticket: https://core.trac.wordpress.org/ticket/62895

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[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: 59907
GitHub commit: 4452b67

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