ToolsPanel: improve unit tests

[ciampo]

What

Improve unit tests by partially rewriting them. They should not be checking implementation details (like classnames, the presence of certain react components...), but instead, they should test the ToolsPanel component replicating the way end-users interact with it.

Why

Here's a great explainer

A/C

• There should be no usages of querySelector, querySelectorAll or any similar way of getting an element from the DOM.
• Similarly, we should not test the exact DOM structure (e.g. getting parent elements, or checking for the existence of a specific React component). We should instead, for example, find components by role, or accessible text
• Add coverage for behaviour related to unique panelIds to cover the user behaviour of switching between similar blocks that share common ToolsPanels. A concrete example is to cover the bug fix in ToolsPanelItem: Add panelId check before calling toggle methods #35375

[aaronrobertshaw]

A PR has been created addressing as much as possible from the list in the description: #35658