Performance tests for chained flow operations

Also, remove common definitions for thread-builders list, moving
parameter definitions to the tests themselves to improve clarity.

Test: atest -c StructuredConcurrencyPerfTests --test-filter '.*FlowOperatorChainBenchmark'
Bug: 404377320
Flag: EXEMPT test
Change-Id: I33c320f13784d24bf11fec371ee3e9b41d48d350