Auto-generate query names for anonymous GraphQL queries

For the type generation to work, GraphQL queries have to have a unique name.

works:

query GetCustomer {
  customer {
    firstName
    lastName
  }
}

doesn't work:

query {
  customer {
    firstName
    lastName
  }
}

Since we control the type generation and have access to the originating file name, contents, etc. it would be possible to auto-generate missing query names. This should be behind a configuration flag, but if it turns out to be viable and stable it should be enabled by default with a possibility to opt-out.

Name generation has to be unique enough that multiple queries can be created in the same file without a name and still get the correct types.

Start by locating the type-generation entry point and existing configuration handling, then trace how the originating file and query contents are passed through. Add focused coverage for multiple anonymous queries in one file and for the configuration flag; done means generated types remain correctly associated with unique generated names and named queries continue to work.