LSIF: GraphQL enhancements
Created by: efritz
This PR improves the LSIF GraphQL API:
- removes LSIFDump and LSIFJob as these can just get a node directly by identifier
- moves LSIFDump under Repository resolver
This PR also changes code structure a bit:
- a8n and codeintel resolvers are no longer assigned to
schemaResolver, but to aOptionalResolversstruct defined in the graphqlbackend package. This is necessary as the repositoryResolver (which is created directly in many places) also needs a reference to these optionally assigned resolvers (and there is no current way to pass them from the schema resolver as repository resolvers can be created independently).