[FIX] Charts: Ensure Chart js extension are loaded on chart creation

[rrahir]

When calling the method chartToImage, the chartJs extensions might not be loaded as we load them conditionally when mounting a chart. Hence, calling ChartToImage when there are no visible charts in the viewport or if we just instantiate a model without loading a component Spreadsheet, the extensions will be missing.

Right now, the plugins/extensions are not fundamental to convert a chart to an image but this becomes problematic with the arrival of future charts (for instance Funnel).

This commit adds a check to ensure that the extensisons are loaded and unloads them after use as they can cause crashes when using the global ChartJs variable elsewhere (see #6076).

Task: 5214007

Description:

description of this task, what is implemented and why it is implemented that way.

Task: TASK_ID

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

[robodoo]