additionalProperties missing in Schema #790
Description
/ The com.google.genai.types.Schema class (and its Builder) is missing the 'additionalProperties' field.
// This is a critical omission for OpenAPI 3.0 compliance, as it makes it impossible to
// define Map-like structures (objects with dynamic keys) using the native Schema objects.
//
// Expected usage that is currently impossible:
Schema mapSchema = Schema.builder()
.type("object")
.additionalProperties(Schema.builder().type("string").build()) // Method 'additionalProperties' is missing
.build();