fix(executor): handle resolveType correctly for v15

[ardatan]

Fixes #6279

Since the executor is version agnostic, it should respect the schemas created with older versions.

So if a type resolver returns a type instead of type name which is required since graphql@16, the executor should handle it correctly.

See the following example:

// Assume that the following code is executed with `graphql@15`
import { execute } from '@graphql-tools/executor';

const BarType = new GraphQLObjectType({
  name: 'Bar',
  fields: {
    bar: {
      type: GraphQLString,
      resolve: () => 'bar'
    }
  }
});
const BazType = new GraphQLObjectType({
  name: 'Baz',
  fields: {
    baz: {
      type: GraphQLString,
      resolve: () => 'baz'
    }
  }
});
const BarBazType = new GraphQLUnionType({
  name: 'BarBaz',
  types: [BarType, BazType],
  // This is the resolver that returns the type instead of type name
  resolveType(obj) {
    if ('bar' in obj) {
      return BarType;
    }
    if ('baz' in obj) {
      return BazType;
    }
  }
});
const QueryType = new GraphQLObjectType({
  name: 'Query',
  fields: {
    barBaz: {
      type: BarBazType,
      resolve: () => ({ bar: 'bar' })
    }
  }
});
const schema = new GraphQLSchema({
  query: QueryType
});

const result = await execute({
  schema,
  document: parse(
    /* GraphQL */ `
      query {
        barBaz {
          ... on Bar {
            bar
          }
          ... on Baz {
            baz
          }
        }
      }
    `
  )
});

expect(result).toEqual({
  data: {
    barBaz: {
      bar: 'bar'
    }
  }
});

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🦋 Changeset detected

Latest commit: cd1ab96

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@graphql-tools/executor	Patch

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🚀 Snapshot Release (alpha)

The latest changes of this PR are available as alpha on npm (based on the declared changesets):

Package	Version	Info
@graphql-tools/executor	1.2.7-alpha-20240619191149-cd1ab96503149b7ed7feaeae653872e1579a89ca	npm ↗︎ unpkg ↗︎

[github-actions]

✅ Benchmark Results

     ✓ no_errors
     ✓ expected_result

     checks.........................: 100.00% ✓ 332       ✗ 0  
     data_received..................: 39 MB   3.9 MB/s
     data_sent......................: 142 kB  14 kB/s
     http_req_blocked...............: avg=4.17µs  min=1.98µs   med=2.63µs   max=203.65µs p(90)=3.86µs   p(95)=4.26µs  
     http_req_connecting............: avg=827ns   min=0s       med=0s       max=137.28µs p(90)=0s       p(95)=0s      
     http_req_duration..............: avg=56.26ms min=48.09ms  med=52.26ms  max=150.1ms  p(90)=61.98ms  p(95)=87.13ms 
       { expected_response:true }...: avg=56.26ms min=48.09ms  med=52.26ms  max=150.1ms  p(90)=61.98ms  p(95)=87.13ms 
     http_req_failed................: 0.00%   ✓ 0         ✗ 166
     http_req_receiving.............: avg=132.7µs min=109.74µs med=129.33µs max=252.84µs p(90)=147.61µs p(95)=154.35µs
     http_req_sending...............: avg=25.72µs min=17.68µs  med=23.8µs   max=116.8µs  p(90)=31µs     p(95)=35.06µs 
     http_req_tls_handshaking.......: avg=0s      min=0s       med=0s       max=0s       p(90)=0s       p(95)=0s      
     http_req_waiting...............: avg=56.1ms  min=47.95ms  med=52.11ms  max=149.77ms p(90)=61.83ms  p(95)=86.97ms 
     http_reqs......................: 166     16.557178/s
     iteration_duration.............: avg=60.37ms min=51.57ms  med=56.31ms  max=153.93ms p(90)=66.45ms  p(95)=91.82ms 
     iterations.....................: 166     16.557178/s
     vus............................: 1       min=1       max=1
     vus_max........................: 1       min=1       max=1

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