This commit adds methods to easily obtain calendar validity per resource
for a given search period and get the work intervals per resource,
taking into account the validity of their calendars.
In hr, the create and departure date of an employee are taken into
account to compute the calendars validity.
In hr_contract, it looks for every contract of human resources with
employee of type student or employee existing in the search period and
consider the specific calendar of the contract as valid during the
contract-lifetime.
PR: #77362
task-2646630
Thibault Libioulle
74624f43ee