Avoid PhabricatorApplicationTransactionStructureException on editors not supporting Mute Notifications

Summary:
Do not expose the "Mute Notifications" sidebar menu entry when the underlying Editor for that object type does not support muting notifications (means: creating a transaction of type "core:edge") at all.
This avoids a disappointing PhabricatorApplicationTransactionStructureException after two clicks.

Disabling the menu entry while still exposing it makes no sense here as the user could never get it enabled anyway.

EXCEPTION: (PhabricatorApplicationTransactionStructureException) Attempting to apply a transaction (of class "PhabricatorFileTransaction", with type "core:edge") which has not been constructed correctly: Transaction has type "core:edge", but that transaction type is not supported by this editor (PhabricatorFileEditor). at [<phorge>/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php:1830]

EXCEPTION: (PhabricatorApplicationTransactionStructureException) Attempting to apply a transaction (of class "LegalpadTransaction", with type "core:edge") which has not been constructed correctly: Transaction has type "core:edge", but that transaction type is not supported by this editor (LegalpadDocumentEditor). at [<phorge>/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php:1830]

Closes T15378

Test Plan:

• Open various different object types:
  • Files: http://phorge.localhost/F1 (not implemented)
  • Legalpad: http://phorge.localhost/legalpad/view/1/ (not implemented)
  • Maniphest: http://phorge.localhost/T1 (implemented)
• Click "Subscribe" on these various types of objects.
• Click "Mute Notifications" on these various types of objects, remember which objects throw an exception.
• Apply this patch.
• Check that "Mute Notifications" is not exposed for those types of objects that threw an exception.

Reviewers: O1 Blessed Committers, valerio.bozzolan

Reviewed By: O1 Blessed Committers, valerio.bozzolan

Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15378

Differential Revision: https://we.phorge.it/D25730