Rename the public methods in the session tokens API.

Introduces a new get( $token ) method. get_token() would not have made sense and spurred the overall renaming. Public methods are now get, get_all, verify, create, update, destroy, destroy_others, and destroy_all.

The protected abstract methods designed for alternative implementations remain the same.

props mdawaffe.
see #20276.

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Plugin installer: Minor adjustments to aid with discovery.

fixes #29387.

Built from https://develop.svn.wordpress.org/trunk@29636


git-svn-id: http://core.svn.wordpress.org/trunk@29410 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Adjust [29634] so the Upload Plugin button can be shown. see #29236.

Built from https://develop.svn.wordpress.org/trunk@29637


git-svn-id: http://core.svn.wordpress.org/trunk@29411 1a063a9b-81f0-0310-95a4-ce76da25c4cd