Ensure cost directives are picked up when not explicitly imported

[tninesling]

With the recent composition changes, importing @cost results in a supergraph schema with the cost specification import at the top. The @cost directive itself is not explicitly imported, as it's expected to be available based on being the default export from the cost specification. In contrast, uses of @listSize to translate to an explicit import in the supergraph.

This exposed the brittle initial implementation of cost directive handling, which built up a map of directive name aliases from import statements. The core change made to address this issue is to remove the directive name map and replace it with calls to SpecDefinition::directive_name_in_schema, which is equivalent to the change we made on the composition side.

The fallout from this is that we need access to a FederationSchema, which is private to the apollo-federation package. I've pushed the cost directive parsing logic into the CostSpecDefinition to abstract away the import name aliasing while cutting down on the public surface area of the federation package. Now, the consuming plugin can simply pass in a schema and a field to get the relevant directive information.

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[router-perf]

CI performance tests

• connectors-const - Connectors stress test that runs with a constant number of users
• const - Basic stress test that runs with a constant number of users
• demand-control-instrumented - A copy of the step test, but with demand control monitoring and metrics enabled
• demand-control-uninstrumented - A copy of the step test, but with demand control monitoring enabled
• enhanced-signature - Enhanced signature enabled
• events - Stress test for events with a lot of users and deduplication ENABLED
• events_big_cap_high_rate - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity
• events_big_cap_high_rate_callback - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity using callback mode
• events_callback - Stress test for events with a lot of users and deduplication ENABLED in callback mode
• events_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
• events_without_dedup_callback - Stress test for events with a lot of users and deduplication DISABLED using callback mode
• extended-reference-mode - Extended reference mode enabled
• large-request - Stress test with a 1 MB request payload
• no-tracing - Basic stress test, no tracing
• reload - Reload test over a long period of time at a constant rate of users
• step-jemalloc-tuning - Clone of the basic stress test for jemalloc tuning
• step-local-metrics - Field stats that are generated from the router rather than FTV1
• step-with-prometheus - A copy of the step test with the Prometheus metrics exporter enabled
• step - Basic stress test that steps up the number of users over time
• xlarge-request - Stress test with 10 MB request payload
• xxlarge-request - Stress test with 100 MB request payload

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