Use monospaced font in Passphrase "Reveal Secret" dialog

Summary: Fixes T10812. Make it easier to disambiguate great passwords like `iI|l1oO()thenumber1nospellitout`.

Test Plan: {F1219074}

Reviewers: chad, yelirekim

Reviewed By: yelirekim

Maniphest Tasks: T10812

Differential Revision: https://secure.phabricator.com/D15715

src/applications/passphrase/controller/PassphraseCredentialRevealController.php

@@ -51,6 +51,7 @@ final class PassphraseCredentialRevealController
             id(new AphrontFormTextAreaControl())
               ->setLabel(pht('Plaintext'))
               ->setReadOnly(true)
+              ->setCustomClass('PhabricatorMonospaced')
               ->setHeight(AphrontFormTextAreaControl::HEIGHT_VERY_TALL)
               ->setValue($secret->openEnvelope()));
       }