fix: Include *(Datum|Value) in SchemaValidationError

[dangotbanned]

Fixes #2913

Examples

import altair as alt

>>> alt.Chart().mark_point().encode(x=alt.datum(1, wrong_argument=1))
SchemaValidationError: `XDatum` has no parameter named 'wrong_argument'

Existing parameter names are:
datum          impute   title   
axis           scale    type    
bandPosition   stack            

See the help for `XDatum` to read the full description of these parameters

import altair as alt

>>> alt.Chart().mark_point().encode(color=alt.value("red", predicate=True))
SchemaValidationError: `ColorValue` has no parameter named 'predicate'

Existing parameter names are:
value   condition   

See the help for `ColorValue` to read the full description of these parameters

Tasks

• Demonstrate on existing tests (8fb2661)
• Add/Update tests (8fb2661), (1d6c844)
• Clean up new SchemaValidationError code (commits)

Future Work

• SchemaValidationError relevance heuristic is flawed #3752