Use most specific class possible in schema validation errors

[binste]

Addresses #2568 (comment)

Works already well but I'll still want to

• Extend existing and add new tests to check if correct class name appears in error message
• Test against multiple jsonschema versions (3, 4, 4.5, 4.16, 4.17)

[binste]

@joelostblom This already works if a wrong argument was passed to an encoding channel. Your example #2568 (comment) works anyway even without this PR because alt.Scale is immediately validated when it's instantiated. Do you have any other examples from #2568 I should test it against?

[joelostblom]

This is looking great! Thanks for getting to it so quickly @binste. I tried a few different examples and they all seem to work fine. One thing that I did notice is that if we use to datum encoding then their message is incorrect:

alt.Chart().mark_point().encode(x=alt.datum(1, wrong_name=1))

SchemaValidationError: Invalid specification

        altair.vegalite.v5.schema.channels.X, validating 'additionalProperties'

        Additional properties are not allowed ('datum', 'wrong_name' were unexpected)

'datum' should not be included above as an incorrect property to the X channel, instead wrong_name should be mentioned as an incorrect parameter to datum. The way to handle this is probably with special error checking inside the datum function, and it is not introduced by this pull request, but I thought I would mention it here anyways. The tests here also look reasonable to me.

[binste]

Good to go from my side. I can review #2568 if you want once you merged in these changes.