feat(gen2-migration): add graphql lambda resolver migration support

[dgandhi62]

This PR adds support for migrating GraphQL Lambda resolvers (functions with @function directives) from Amplify Gen 1 to Gen 2. Previously, the migration tool only handled schema, table mappings, and auth modes but ignored Lambda function resolvers entirely.

Example

Gen 1 GraphQL Schema:

type Query {
  customResolver: String @function(name: "myCustomFunction")
  calculator: Int @function(name: "mathFunction")
}

type Todo @model {
  id: ID!
  title: String!
}

Gen2 GraphQL Schema

import { defineData } from '@aws-amplify/backend';
import { myCustomFunction } from './myCustomFunction/resource';
import { mathFunction } from './mathFunction/resource';

const schema = `
  type Query {
    customResolver: String @function(name: "myCustomFunction")
    calculator: Int @function(name: "mathFunction")
  }
  
  type Todo @model {
    id: ID!
    title: String!
  }
`;

export const data = defineData({
  schema,
  functions: {
    myCustomFunction: myCustomFunction,
    mathFunction: mathFunction
  }
});