preferredMimeType is text/plain, even for widgets

[rowanc1]

On the newest version (v1.1.1) the widgets are not working for me in development or on binder.

I think that this has to do with when we choose to show the text-renderer (see #104), which gets chosen more often than it should.

For the line:

const preferredMimeType = rendermime.preferredMimeType(mimeBundle ?? {});

We should probably have the second argument, I think, as "any":

How to consider safe/unsafe factories. If 'ensure', it will only consider safe factories. If 'any', any factory will be considered. If 'prefer', unsafe factories will be considered, but only after the safe options have been exhausted.

With safe=undefined:

With safe="any" - the fix!

const preferredMimeType = rendermime.preferredMimeType(mimeBundle ?? {}, 'any');