This cleans up the `Router` code and adds a bunch of tests. These sorts of systems are a real pain to test, since they have a bunch of asynchronous goroutines living their own lives, so the test coverage is decent but not fantastic. Luckily we've been able to move all of the complex peer management and transport logic outside of the router, as synchronous components that are much easier to test, so the core router logic is fairly small and simple.

This also provides some initial test tooling in `p2p/p2ptest` that automatically sets up in-memory networks and channels for use in integration tests. It also includes channel-oriented test asserters in `p2p/p2ptest/require.go`, but these have primarily been written for router testing and should probably be adapted or extended for reactor testing.

This tightens up the `PeerManager` and related code, adds a ton of tests, and fixes a bunch of inconsistencies and bugs.

blockchain/vX reactor priority was decreased because during the normal operation
(i.e. when the node is not fast syncing) blockchain priority can't be
the same as consensus reactor priority. Otherwise, it's theoretically possible to
slow down consensus by constantly requesting blocks from the node.

NOTE: ideally blockchain/vX reactor priority would be dynamic. e.g. when
the node is fast syncing, the priority is 10 (max), but when it's done
fast syncing - the priority gets decreased to 5 (only to serve blocks
for other nodes). But it's not possible now, therefore I decided to
focus on the normal operation (priority = 5).

evidence and consensus critical messages are more important than
the mempool ones, hence priorities are bumped by 1 (from 5 to 6).

statesync reactor priority was changed from 1 to 5 to be the same as
blockchain/vX priority.

Refs https://github.com/tendermint/tendermint/issues/5816

After a reactor has failed to parse an incoming message, it shouldn't output the "bad" data into the logs, as that data is unfiltered and could have anything in it. (We also don't think this information is helpful to have in the logs anyways.)

`abci.Client`:

- Sync and Async methods now accept a context for cancellation
    * grpc client uses context to cancel both Sync and Async requests
    * local client ignores context parameter
    * socket client uses context to cancel Sync requests and to drop Async requests before sending them if context was cancelled prior to that

- Async methods return an error
    * socket client returns an error immediately if queue is full for Async requests
    * local client always returns nil error
    * grpc client returns an error if context was cancelled before we got response or the receiving queue had a space for response (do not confuse with the sending queue from the socket client)

- specify clients semantics in [doc.go](https://raw.githubusercontent.com/tendermint/tendermint/27112fffa62276bc016d56741f686f0f77931748/abci/client/doc.go)

`mempool.TxInfo`

- add optional `Context` to `TxInfo`, which can be used to cancel `CheckTx` request

Closes #5190

Refs #2888

Reduces the state sync discovery time from 20 to 15 seconds, and makes it configurable.

On startup, the peer-to-peer stack may have peers connected before the state sync process begins, causing these to not trigger `AddPeer` events and thus not be used for snapshot discovery. Broadcasting a snapshot request to these explicitly makes sure we discover snapshots from existing peers as well.

## Description

This PR wraps the stdlib sync.(RW)Mutex & godeadlock.(RW)Mutex. This enables using go-deadlock via a build flag instead of using sed to replace sync with godeadlock in all files

Closes: #3242

## Description



Closes: #XXX

Fixes #828. Adds state sync, as outlined in [ADR-053](https://github.com/tendermint/tendermint/blob/master/docs/architecture/adr-053-state-sync-prototype.md). See related PRs in Cosmos SDK (https://github.com/cosmos/cosmos-sdk/pull/5803) and Gaia (https://github.com/cosmos/gaia/pull/327).

This is split out of the previous PR #4645, and branched off of the ABCI interface in #4704. 

* Adds a new P2P reactor which exchanges snapshots with peers, and bootstraps an empty local node from remote snapshots when requested.

* Adds a new configuration section `[statesync]` that enables state sync and configures the light client. Also enables `statesync:info` logging by default.

* Integrates state sync into node startup. Does not support the v2 blockchain reactor, since it needs some reorganization to defer startup.