node: refactor package node (#21105)

This PR significantly changes the APIs for instantiating Ethereum nodes in
a Go program. The new APIs are not backwards-compatible, but we feel that
this is made up for by the much simpler way of registering services on
node.Node. You can find more information and rationale in the design
document: https://gist.github.com/renaynay/5bec2de19fde66f4d04c535fd24f0775.

There is also a new feature in Node's Go API: it is now possible to
register arbitrary handlers on the user-facing HTTP server. In geth, this
facility is used to enable GraphQL.

There is a single minor change relevant for geth users in this PR: The
GraphQL API is no longer available separately from the JSON-RPC HTTP
server. If you want GraphQL, you need to enable it using the
./geth --http --graphql flag combination.

The --graphql.port and --graphql.addr flags are no longer available.

# Conflicts:
#	cmd/faucet/faucet.go
#	cmd/geth/chaincmd.go
#	cmd/geth/config.go
#	cmd/geth/consolecmd.go
#	cmd/geth/main.go
#	cmd/utils/flags.go
#	cmd/wnode/main.go
#	core/rawdb/freezer.go
#	eth/api_backend.go
#	eth/backend.go
#	ethclient/ethclient_test.go
#	ethstats/ethstats.go
#	graphql/service.go
#	internal/ethapi/backend.go
#	les/api_backend.go
#	les/api_test.go
#	les/checkpointoracle/oracle.go
#	les/client.go
#	les/commons.go
#	les/server.go
#	miner/stresstest/stress_clique.go
#	miner/stresstest/stress_ethash.go
#	mobile/geth.go
#	node/api.go
#	node/node.go
#	node/node_example_test.go
#	node/node_test.go
#	node/rpcstack.go
#	node/rpcstack_test.go
#	node/service.go
#	node/service_test.go
#	node/utils_test.go
#	p2p/simulations/examples/ping-pong.go
#	p2p/testing/peerpool.go
#	p2p/testing/protocolsession.go
#	p2p/testing/protocoltester.go
#	whisper/mailserver/server_test.go
#	whisper/whisperv6/api_test.go
#	whisper/whisperv6/filter_test.go
#	whisper/whisperv6/whisper.go
#	whisper/whisperv6/whisper_test.go