[REF] tests: remove chart snapshot tests

[hokolomopo]

Description

There were a dozen chart snapshot tests in chart_plugin.test.ts. Some tests were relying exclusively on snapshots.

The main issue is that snapshots don't actually test a feature. Reading the test provides no insight on what is actually tested, and after years of snapshot updates, who's to say that the relevant part of the snapshot hasn't changed ? Or that the 400 lines of snapshot for a new test were ever fully reviewed ?

Snapshots shouldn't be the main way a feature is tested. This commit removes most snapshot tests, and replaces them with more explicit expect matchers.

Some snapshots were kept because a snapshot test is still useful as an alarm bell for the coder/reviewer (eg. "why has this pie bar fix changed snapshots of bar charts ?"). But having a dozen snapshot is pointless, making it more likely that the changes are never reviewed.

Task: 5160031

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]