Before this commit, the `getFirstElementForXpath` function is used in
the unit test for the burndown chart. This function is used to select a
HTMLELement with xpath expression and could be used outside the unit
test of the burndown chart.
This commit externalizes this function in a project test utils JS file
to use this function in another unit tests file if needed.
task-2924268
closesodoo/odoo#97574
Related: odoo/enterprise#30173
Signed-off-by: Laurent Stukkens (ltu) <ltu@odoo.com>
