Before this commit, to render the table, the project task list
view computed the list of selected records once for each cell,
and then iterated over that selection to check whether selected
tasks were all associated with the same project (to set the
stage_id field readonly if not). However, computing the selection
requires to iterate over all records, so the rendering was O(n^2).
As a consequence, the rendering of (not so) large tables was very
slow (~1s for 80 records).
With this commit, we compute only once for the whole table whether
the selection contains records from different projects.
closesodoo/odoo#153611
Signed-off-by: Géry Debongnie <ged@odoo.com>