Perform IRI validation for base IRI and class fields

[wouterbeek]

Observed

Currently IRI validation is performed when entering property IRIs, but not when entering base IRIs or class IRIs.

Expected

All IRI fields to be validated, including the base IRI and class fields.

Steps to reproduce

1. Enter a text that is not a valid IRI in either the base IRI or class field.
2. Export to RDF and notice that the resulting export is not valid.

[LaurensRietveld]

This is an unresolved issue atm:

• There is no reliable IRI validation library
• Other places where we do validate IRIs, we actually validate them as URIs

For consistency reasons, we should go for one of the two options below:

• Removing all validation, considering we cannot validate IRIs reliably
• Using URI validation consistently

Leaving this one open for now, and let's revisit once we've made a decision

[MPvHarmelen]

See also https://www.npmjs.com/package/uri-js for IRI parsing and serialization (but not validation)

[wouterbeek]

It is unfortunate that validating IRIs is an unsolved computer science problem in 2022 :-P

We should still apply URI validation (many off-the-shelf libraries for that, probably in the standard library for ECMAScript).