Improve Tab Error handling

[nikku]

Is your feature request related to a problem? Please describe.

Tabs may throw errors and technically we got the EditorTab to handle errors gracefully and propagate them. Unfortunately triggering an actual error, e.g. by inserting a line such as

throw new Error('FOO');

into a tab constructor, e.g. the BpmnTab is not properly handled and results in the app being unmounted.

Describe the solution you'd like

• Tab errors are handled gracefully
• Logged to log panel
• A error placeholder is shown to the user in place of the defective tab

Describe alternatives you've considered

None.

[barmac]

The reason why we don't handle errors gracefully is that EditorTab is an incomplete error boundary. Namely, it does not implement static getDerivedStateFromError.
Cf. https://reactjs.org/docs/error-boundaries.html; also this codesandbox https://codesandbox.io/s/202l1xyk0r?fontsize=14

[nikku]

The reason why we don't handle errors gracefully is that EditorTab is an incomplete error boundary. Namely, it does not implement static getDerivedStateFromError.

We don't have to implement getDerivedStateFromError. It should be sufficient to unmount the broken editor (replacing it with an ErrorTab or the like).

[nikku]

Suggestion: Find an icon to make someones day, if the editor fails, e.g. https://thenounproject.com/term/open-source/?search=error

Caveat: We need to make sure we use free icons or provide proper attribution.

[barmac]

Note: Enzyme does not support getDerivedStateFromError yet (enzymejs/enzyme#1553 (comment)). Because of this, the tests will be a bit different from what we already have in our code base.