Fix a type definitions for response_schema and function calling

[ashphy]

Description

This PR fixes the type definitions of response schema for JSON output and function calling parameters.

Background

The current type definition cannot represent all the schemas defined in the API. For example, the following schema definition results in a type error.

const generationConfig: GenerationConfig = {
  responseMimeType: "application/json",
  responseSchema: {
    type: FunctionDeclarationSchemaType.OBJECT,
    properties: {
      list: {
        type: FunctionDeclarationSchemaType.ARRAY,
        items: {
        // error TS2353: Object literal may only specify known properties, 
        // and 'items' does not exist in type 'FunctionDeclarationSchema'
          type: FunctionDeclarationSchemaType.STRING,
        },
      },
    },
    required: ["list"],
  },
};

Problem

The type definition of Schema does not match the API.

generative-ai-js/packages/main/types/function-calling.ts

Lines 108 to 130 in 5739e2a

	export interface Schema {
	/**
	* Optional. The type of the property. {@link
	* FunctionDeclarationSchemaType}.
	*/
	type?: FunctionDeclarationSchemaType;
	/** Optional. The format of the property. */
	format?: string;
	/** Optional. The description of the property. */
	description?: string;
	/** Optional. Whether the property is nullable. */
	nullable?: boolean;
	/** Optional. The items of the property. {@link FunctionDeclarationSchema} */
	items?: FunctionDeclarationSchema;
	/** Optional. The enum of the property. */
	enum?: string[];
	/** Optional. Map of {@link FunctionDeclarationSchema}. */
	properties?: { [k: string]: FunctionDeclarationSchema };
	/** Optional. Array of required property. */
	required?: string[];
	/** Optional. The example of the property. */
	example?: unknown;
	}

items and properties should be the Schema itself.
FunctionDeclarationSchema has no items parameter.

generative-ai-js/packages/main/types/function-calling.ts

Lines 136 to 145 in 5739e2a

	export interface FunctionDeclarationSchema {
	/** The type of the parameter. */
	type: FunctionDeclarationSchemaType;
	/** The format of the parameter. */
	properties: { [k: string]: FunctionDeclarationSchemaProperty };
	/** Optional. Description of the parameter. */
	description?: string;
	/** Optional. Array of required parameters. */
	required?: string[];
	}

Schema definitions

The type definitions refer to the following specifications:

• GenerationConfig (for JSON output)
  • https://cloud.google.com/vertex-ai/docs/reference/rest/v1/GenerationConfig
• Tool (for Function Calling)
  • https://cloud.google.com/vertex-ai/docs/reference/rest/v1/Tool#FunctionDeclaration

Both parameters refer to the Schema object:

• https://cloud.google.com/vertex-ai/docs/reference/rest/v1/Schema

How Has This Been Tested?

Added a test case

References

• Function calling #32
• Add responseSchema to generationConfig #158

[ashphy]

Closed due to conflict with #222, The owners never did review this.