test: compare GraphQL with Prettier

tests/oracle/graphql.ts formats Prettier's fixtures, pretty_graphql's
tests and target/corpus/graphql with Prettier and with tidy, under four
option sets, and checks that tidy's output reads back the same.
mise run corpus:graphql builds the corpus: GitLab's 2,507 GraphQL files
and the schemas of GitHub, Saleor, Artsy, SWAPI and Sourcegraph.