Adds fork-awareness and finalization notifications to transaction pool watchers. (#4740)

* adds finalization support to sc-transaction-pool using MaintainedTransactionPool for finalization events

* adds TransactionStatus::Retracted, notify watchers of retracted blocks, finalized now finalizes, transactions for current finalized -> last finalized block

* adds last_finalized to ChainApi, use generic BlockT for ChainEvent

* fix tests

* Apply suggestions from code review

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* tests

* fix tests, docs, lazily dedupe pruned hashes

* fix tests, Cargo.lock

* Apply suggestions from code review

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* remove tree_route, last_finalized from ChainApi, add block hash to Finalization and Retracted events

* prune finality watchers

* fix tests

* remove HeaderBackend bound from FullChainApi

* code style nits, terminate stream in finality_timeout

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

substrate/Cargo.lock

@@ -6263,6 +6263,7 @@ dependencies = [
  "serde_json",
  "sp-core",
  "sp-rpc",
+ "sp-runtime",
  "sp-transaction-pool",
  "sp-version",
 ]
@@ -6424,11 +6425,13 @@ dependencies = [
  "criterion 0.3.1",
  "derive_more",
  "futures 0.3.4",
+ "linked-hash-map",
  "log 0.4.8",
  "parity-scale-codec",
  "parity-util-mem",
  "parking_lot 0.10.0",
  "serde",
+ "sp-blockchain",
  "sp-core",
  "sp-runtime",
  "sp-transaction-pool",
@@ -7644,6 +7647,7 @@ dependencies = [
  "parity-scale-codec",
  "parking_lot 0.10.0",
  "sc-transaction-graph",
+ "sp-blockchain",
  "sp-runtime",
  "sp-transaction-pool",
  "substrate-test-runtime-client",