When accepting the policies via the sitepolicy handler, only compulsory
policies are to be marked as accepted. Optional policies will be left as
pending. Users must express their consent explicitly for them.
As a side product of the change, unit tests are added for the whole
handler class.
This method allows to quickly check if the given policy version is
marked as optional or compulsory. This will be needed in other places
such as permissions check.
The method now returns three-state logic. A bool value true/false is
returned if the user has accepted/rejected the policy, respectively. A
null value is returned if the user did not express their agreement in
either way yet.
This allows to distinguish between "rejected the policy" and "did not
say anything about it yet" cases.
The policies can be revoked by clicking the "Agreed [on behalf]" ticks.
A message has been added also to explain users they must contact to
the DPO if they want to withdraw their consent to policies.
Avoid redirection for accepting new policies during the manager user session
when $user->policyagreed=0 and he/she activates the first policy for logged in users.
Part of MDL-61864
