API: Add the ability to flag parameter values as deprecated

API: Add the ability to flag parameter values as deprecated

This has a number of implications:
* A deprecation warning is automatically generated if the value is used.
* action=paraminfo can list it in a machine-readable manner.
* It is automatically flagged in the help when message-per-value mode is
  used.
* In values lists in the help, it's specially marked (currently
  strike-through).
* ApiSandbox will mark it in the widgets (currently strike-through).

Deprecation of submodules is not automatically detected here, that's
left for a later patch.

Bug: T123931
Change-Id: Idad6377063e457f9352a99df5c7cc15b1563579e