[FIX] web: measure/groupby many2one variation in pivot view

In case a many2one field (let us say 'foo') is used
simultaneously as a groupby and a measure in the pivot view,
the values returned by a read_group for that many2one are of
the form [id, label] and the aggregated values (always 1) are
missing in the read_group results (datapoints).
Thus typically, a datapoint is of the form

{'foo': [1, 'Bar'], '__count': 4, ...}

and does not contain information on the 'foo:count_distinct'
value (this is a read_group bug).

As a consequence, a special processing of the read_group
datapoints is done in the pivot model to handle that
situation and the value for 'foo:count_distinct' is infered
correctly to be 1.

In the pivot comparison mode, datapoints comming from the
period and the comparison period (data and comparisonData
sets) are identified if they have same values for the groupby
fields and the measure values become small objects containing
information on the the measure values for data and for
comparisonData and on the related variation.

Thus

{foo: [1, 'Bar'], __count: 4, ...}

from data and

{foo: [1, 'Bar'], __count: 3, ...}

from comparisonData should become a single datapoint

{
foo: [1, 'Bar'],
__count: {
data: 4,
comparisonData: 3,
variation: {
magnitude: +33 (%)
}
}
fooAggregate: {
data: 1,
comparisonData: 1,
variation: {
magnitude: 0 (%)
}
}

It turns out that the code responsible for merging the data
and comparison datapoints made a mistake by mixing the keys
'foo' and 'fooAggregate', with the consequence that the
variations were not correctly computed in the situation
described above.

This is fixed in this commit.

closes odoo/odoo#33118

Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>