Upgrade/Install: Only display the auto-update links on the Network Admin >...

Upgrade/Install: Only display the auto-update links on the Network Admin > Themes screen for themes that support the feature.

Follow-up to [48669], [48688].

Props afragen, pbiron, audrasjb, desrosj, SergeyBiryukov.
Merges [48899] to the 5.5 branch.
Fixes #51129.
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git-svn-id: https://core.svn.wordpress.org/branches/5.5@48662 1a063a9b-81f0-0310-95a4-ce76da25c4cd