[FW][FIX] chart: cumulative not working for linear charts

[fw-bot]

Description

The cumulative chart option was not working for line charts with a linear/time axis.

This was because the data in the linear charts runtime was an array of objects {x, y} rather than an array of numbers, and this wasn't properly handled in the cumulative computations.

Task: : 4028957

review checklist

• [ ] feature is organized in plugin, or UI components
• [ ] support of duplicate sheet (deep copy)
• [ ] in model/core: ranges are Range object, and can be adapted (adaptRanges)
• [ ] in model/UI: ranges are strings (to show the user)
• [ ] undo-able commands (uses this.history.update)
• [ ] multiuser-able commands (has inverse commands and transformations where needed)
• [ ] new/updated/removed commands are documented
• [ ] exportable in excel
• [ ] translations (_t("qmsdf %s", abc))
• [ ] unit tested
• [ ] clean commented code
• [ ] track breaking changes
• [ ] doc is rebuild (npm run doc)
• [ ] status is correct in Odoo

Forward-Port-Of: odoo/o-spreadsheet#4583 Forward-Port-Of: odoo/o-spreadsheet#4568

[robodoo]

[fw-bot]

This PR targets saas-17.3 and is part of the forward-port chain. Further PRs will be created up to master.

More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port

[fw-bot]

@hokolomopo @pro-odoo ci/runbot failed on this forward-port PR

[hokolomopo]

@robodoo r+

[fw-bot]

@hokolomopo @pro-odoo this PR was modified / updated and has become a normal PR. It must be merged directly.