proposal: Schema.SubSchema

[jba]

Add the following method:

// SubSchema returns the sub-schema of root selected by the given [JSON Pointer] expression.
// It returns nil if the expression does not refer to a schema.
//
// [JSON Pointer]: https://datatracker.ietf.org/doc/html/rfc6901
func (root *Schema) SubSchema(jp string) *Schema

[jba]

This should be a simple call of dereferenceJSONPointer, in json_pointer.go.