[IMP] chart: avoid overlapping values on charts

[hokolomopo]

Description

The option "Show Values" on charts could lead to overlapping texts in the chart, which was quite ugly.

This commit improve the behaviour or the value labels:

• prevent overlapping value labels on stacked charts
• the bar chart value labels are now in the middle of the bar
• the value labels have now the same color as the dataset
• prevent value labels from going outside of the chart

Code-wise, the commit totally splits the handling of bar and horizontal bar charts. It make the code slightly longer, but avoid having to write a ternary for each computation of x/y position, which ultimately makes the code more readable.

Task: 4207889

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