Improve safety + autocomplete for @arktype/schema definitions

[ssalbdivad]

There is currently a validateSchema type but generally we just accept a SchemaDef in most places, which accept extra keys and doesn't e.g. narrow constraints based on basis type.

We should standardize these APIs to use the validateSchema approach to avoid extra keys and give more precise hints about what is allowed based on an intersection basis, ideally also reintegrating some of the commented test cases for e.g. prop and tuple inference which is not handled.