Accrual plan for leave days gets blocked, even when the remaining leave balance is below the cap. As a result, no additional leaves are accrued beyond a certain point, even though they should be.

# Steps to reproduce:
Go to time off app
* Create a new leave type.
* Create a new accrual plan with:
        - one milestone :
		- 2 days accrued per month
		- Cap: 10 days
		- start accruing 1 days after
		- No expiration
		- Carry over: All
* Create and validate a leave allocation 
       - 1 year ago
       - new leave type
       - new accrual plan
* Take the maximum number of leaves available.
* Advance the computer calendar by 1 year.
* Again, take the maximum number of leaves.
* Advance the computer calendar by another year.
* Try to take a future leave.
-> Issue: It’s not possible to take a future leave, the number of accrued days has stopped increasing. The accrual plan appears blocked.

Objective : The accrual plan should continue to allocate leave days even if leaves have been consumed regularly, as long as the remaining leaves are under the cap.

## Issue
Before going further: the property `leaves_taken` of the `hr.leave.allocation` is supposed to contain the number of leaves this allocation cover until "today".

In the `_test_get_allocation_future_leaves1` added test, in the last line of the test :
`assert_virtual_leaves_equal(self, leave_type_day, 2, self.employee_emp, date='2023-02-01')`

When calling `get_allocation_data` with a `target_date` set in the future, the result is wrong. Here is how it works :
`get_allocation_data`
...
.....`_get_consumed_leaves` (1)
...........`_get_future_leaves_on` (2)
...............`_process_accrual_plans` (3)
....................`_compute_leaves` (4)
.........................`_get_consumed_leaves` (5)
..............................`get_future_leaves_on` (6)
...................................`process_accrual_plans` (7)

**A)** The method **(2)** try to calculate the added number of days each allocation will have on `target_date`. So it creates a copy of the allocation in memory using the 'new' method:
`fake_allocation = self.env['hr.leave.allocation'].with_context(default_date_from=accrual_date).new(origin=self)`
It will then update it to `target_date` using `_process_accrual_plans` and will return the difference of days between the
updated `fake_allocation` and the current allocation (`self`)

**B)** Before iterating over each accrual date, the `_process_accrual_plans` **(3)** will get the `leaves_taken` property which is a computed field. It will trigger `_compute_leaves`.

**C)** The method **(4)** will call `_get_consumed_leaves`, and so the nightmare begins.

**D)** The method **(6)** will create a second `fake_allocation` based on the origin of the first `fake_allocation` (see **A)**).

**E)** This time, `_process_accrual_plans` **(7)** will also look at the `leaves_taken`, but won't trigger the `_compute_leaves` probably because the current allocation is a `fake_allocation` of a `fake_allocation`, and one property of the `new` method is that `Two new records with the same origin record are considered equal.`. Therefore, the `leaves_taken` is considered to be already computed (but it's not).

So `_process_accrual_plans` read the `leaves_taken` which is 0 (probably the default value of `leaves_taken`), but it should be 20 !

**F)** As the value of `leaves_taken` is wrong, the fake_allocation n°2 is also wrong, and its `number_of_day` is 10 but the `number_of_days` of the origin allocation is 20. So `get_future_leaves_on` **(6)** will return -10 which makes no sense, and all the previous calls computations will be wrong. And the final `virtual_remaining_leaves` value will be 0 instead of 2.

## Source of the issue
In the `_process_accrual_plans` method, for each allocation, `leaves_taken` is only computed once at the start of the loop over the allocation "important" dates (see `nextcall` property of `hr.leave.allocation`). At this moment, the method calculates the `leaves_taken` the allocation will have on the `accrual_date` parameter. Yet, this property can change depending on the date the allocation is on (`nextcall` property) which leads to some issues in the computation of the `allocation.number_of_days`.

## Solution
For each allocation, compute the `leaves_taken` at every iteration trough the values of `nextcall`. BUT, this can trigger an infinite loop as computing `leaves_taken` calls `_get_consumed_leaves` which calls `_get_future_leaves_on`, which calls `_process_accrual_plans` ... To avoid this, this PR add the context variable `precomputed_allocations` (will be converted into a function parameter in master) which will prevent `_get_consumed_leaves` from calling `_get_future_leaves_on` for the allocations already up to date (contained by this very `precomputed_allocations` context variable).

**For r+: Needs a few changes at 18.0 (hours per day of employee is retrieved differently for example)**

opw-4934391
opw-5226806