Add share intent for mastodon redirect support

[kaosine]

Currently mastodon redirect(see zacharee/MastodonRedirect#23) is unable to redirect to yuito due to lack of support for share intent according to the closed issue that references the linked issue. This would allow for links to various mastodon instances to redirect into yuito on Android.

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• I searched or browsed the repo’s other issues to ensure this is not a duplicate.

[moriel5]

I had accidentally posted this request in the upstream Tusky a long time ago, and it has recently been merged there, so if Yuito gets updated, it should be very easy to add this by simply importing the upstream merges.