Refactor the block requests, finality requests, and light client requests networking protocol to use the new generic request-response system

[tomaka]

This issue is not about any new functionality but about simplifying the existing code.

The following modules should be refactored to use the new request-responses system as their underlying implementation:

• sc_network::block_requests (See client/network: Use request response for block requests #7478)
• sc_network::finality_requests (See grandpa: remove light-client specific block import pipeline #7546)
• sc_network::light_client_handler (See client/network: Use request response for light client requests #7895)