[REQUEST] Make it more obvious when you're viewing an invalid document

[paulwarren-wk]

What should we change and why?

Spun out of #435 and closely related to https://github.com/Arelle/Arelle/issues/760

We want the viewer to cope with at least some types of XBRL invalidity so that it can be used to review reports that are still being prepared.

I think we should make it clearer to users when opening an invalid report, as ignoring some types of error, such as a failure to load a taxonomy file, can lead to confusing results in the viewer. Also, outside of a controlled, pre-release review process, it's unhelpful for XBRL interoperability to silently ignore errors that other tools may treat as fatal.

Possible solutions:

• Require a --ignore-xbrl-errors flag on the CLI in order to proceed in the presence of spec-level errors
• Require a dialog to be dismissed when preparing a viewer in the GUI if there are spec-level errors
• Default to showing the "this document has errors" dialog on load, if there are spec-level errors.

I also think it would be helpful to enumerate the specific types of invalidity that we want to tolerate, as we've had quite a few bugs like #435 where the viewer has made assumptions that only reliable if the document is valid.