dev/core#2141 - Tighten up new page `civicrm/oauth-client/return`

dev/core#2141 - Tighten up new page `civicrm/oauth-client/return`

Overview
--------

The route `civicrm/oauth-client/return` is added in 5.32 as the main "Redirect URL".

In normal usage, the page shouldn't be visible to a user (because the
developer should define some alternative UI) -- but one might see it (a)
during development, (b) if there's an error, or (c) if a clever user mucks
about.

Improvements:

* Error handling
    * Present error messages more nicely
    * Record errors in the log
    * Report more info via hook_oauthReturnError
* Other UI
    * Redact token details (dependent upon permission `manage OAuth client secrets`)
    * Set a more sensibile page title
    * Make output blobs conditional and collapsible