R1:5a454cef8a98

Set ActionName to "Created" for PhabricatorTransactions::TYPE_CREATE

Summary:
Explicitly set "Created" as ActionName (to be used as a mail subject line vary prefix) when the transaction type is `PhabricatorTransactions::TYPE_CREATE` to avoid falling back to a generic "Updated" prefix.

Closes T15865

Test Plan: Either create a new task and check the mail subject line prefix (if you have a mail setup in your Phorge instance), or use the debug patch in P45 and check the order of action strengths.

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