graphql-java-support: Bump graphql-java to v15

[sachindshinde]

This PR is an iteration of the changes suggested in #67 (many thanks to the authors and commenters).

Summary of Changes:

• Bump graphql-java to v15 in the pom.xml
• Remove enforceSchemaDirectives(true) from Federation.java
  • Reason: This option was removed in remove the option to have undeclared directives in your SDL graphql-java/graphql-java#1773 to facilitate spec compliance, and now is always true (thankfully we've already done the legwork to not have to worry about this)
• Remove includeExtendedScalarTypes(true) from SchemaTransformer.java
  • Reason: This option was removed in Removing java types as standard scalars graphql-java/graphql-java#1780 to facilitate spec compliance, and now is always true (what were previously known as "extended scalars" in graphql-java are now just regular custom scalars)
• Add a new standard GraphQL directive @specifiedBy to standard directive lists
  • Reason: This directive was added to graphql-java in add custom scalar Specification URL graphql-java/graphql-java#1772 with the spec addition still pending at [RFC] Custom Scalar Specification URIs graphql/graphql-spec#635
  • Note that it's unknown how gateway currently responds to the presence of this directive definition in the federation SDL, but it's assumed that it will eventually behave the same as it does with other standard directive definitions if it doesn't already do so. (This may introduce an issue in the interim that a user wanting to use @specifiedBy with federation will not be able to do so, since federation SDL won't expose the directive definition and the directive definitions the gateway introduces may not have it.)
• Update FederationSdlPrinter to use graphql-java v15's SchemaPrinter
  • Reason: As described in graphql-java-support: Remove federation directive and type definitions from SDL and use stricter SchemaGenerator checks #53 , we use our own printer to avoid printing federation directive definitions and federation type definitions in SDL.
  • Note that the bugfix that we backported in graphql-java-support: Fix grammar violation in graphql-java's SchemaPrinter #52 is no longer needed with graphql-java v15.

Note that this is a backwards incompatible change due to backwards incompatible changes in graphql-java v15's SchemaPrinter.

It'll be easier in this PR to go commit-by-commit. For FederationSdlPrinter, it'll help to compare FederationSdlPrinter.java in the class-copy-and-rename commit to the v15 SchemaPrinter, located at https://raw.githubusercontent.com/graphql-java/graphql-java/v15.0/src/main/java/graphql/schema/idl/SchemaPrinter.java . For the FederationSdlPrinter changes that fix the issue in #53 , it'll help to compare against the respective changes in that PR.

[sachindshinde]

Note that we should test this in our own Apollo infra before releasing

[pcarrier]

?

[sachindshinde]

My IntelliJ's been adding that in for a while, no clue why it keeps doing that (maybe it's because of plugins?).