Refine alignment of old/new token lists

Refine alignment of old/new token lists

The prior commit means that `$context['participantId']` will activate `{event.*}` tokens - in contexts
that use `TokenProcessor`. And the `TokenProcessor` is *somewhat* matched to the older functions.

This twiddles the match-up:

* Provide continuity for the deprecated `CRM_Core_SelectValues::participantTokens()` - so it still
  only returns `{participant.*}` tokens. Borrow the technique which excludes `{domain.*}` tokens.
  This should ensure better continuity for any callers that actually use `CRM_Utils_Token`.

* Update the assertions for the `TokenProcessor` to show that the `{event.*}` tokens are presented in
  participant-related contexts.