refactor: Unify Field Kind and Schema properties (#2414)

## Relevant issue(s)

Resolves #2409

## Description

Unifies the Field Kind and Schema properties.

client/definitions.go

@@ -78,10 +78,6 @@ type FieldDefinition struct {
 	// Must contain a valid value. It is currently immutable.
 	Kind FieldKind
 
-	// Schema contains the schema name of the type this field contains if this field is
-	// a relation field.  Otherwise this will be empty.
-	Schema string
-
 	// RelationName the name of the relationship that this field represents if this field is
 	// a relation field.  Otherwise this will be empty.
 	RelationName string
@@ -102,7 +98,6 @@ func NewFieldDefinition(local CollectionFieldDescription, global SchemaFieldDesc
 		Name:              global.Name,
 		ID:                local.ID,
 		Kind:              global.Kind,
-		Schema:            global.Schema,
 		RelationName:      global.RelationName,
 		Typ:               global.Typ,
 		IsPrimaryRelation: global.IsPrimaryRelation,

client/document.go

@@ -198,6 +198,14 @@ func validateFieldSchema(val any, field SchemaFieldDescription) (any, error) {
 		}
 	}
 
+	if field.Kind.IsObjectArray() {
+		return nil, NewErrFieldOrAliasToFieldNotExist(field.Name)
+	}
+
+	if field.Kind.IsObject() {
+		return getString(val)
+	}
+
 	switch field.Kind {
 	case FieldKind_DocID, FieldKind_NILLABLE_STRING, FieldKind_NILLABLE_BLOB:
 		return getString(val)
@@ -238,12 +246,6 @@ func validateFieldSchema(val any, field SchemaFieldDescription) (any, error) {
 	case FieldKind_NILLABLE_INT_ARRAY:
 		return getNillableArray(val, getInt64)
 
-	case FieldKind_FOREIGN_OBJECT:
-		return getString(val)
-
-	case FieldKind_FOREIGN_OBJECT_ARRAY:
-		return nil, NewErrFieldOrAliasToFieldNotExist(field.Name)
-
 	case FieldKind_NILLABLE_JSON:
 		return getJSON(val)
 	}