Sync: Propagate block announcement data (#7903)

* Sync: Propagate block announcement data

This pr adds a feature to the sync protocol to propagate the data that
we received alongside a block announcement. This is done by adding a
cache that caches the last X block announcement data where X is set to
the number of `in_peers` (giving every peer the chance to send us a
different block). This will be required by parachains to ensure that
even peers who are not connected to a collator receive the data
alongside the block announcement to properly validate it and request the
block.

* Review comment

* Bring back the code and add new variant to ensure we don't insert block
announce data when something wasn't checked

* Also use out_peers

substrate/Cargo.lock

@@ -3366,9 +3366,9 @@ dependencies = [
 
 [[package]]
 name = "lru"
-version = "0.6.1"
+version = "0.6.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "be716eb6878ca2263eb5d00a781aa13264a794f519fe6af4fbb2668b2d5441c0"
+checksum = "3aae342b73d57ad0b8b364bd12584819f2c1fe9114285dfcf8b0722607671635"
 dependencies = [
  "hashbrown",
 ]
@@ -7153,6 +7153,7 @@ dependencies = [
  "linked-hash-map",
  "linked_hash_set",
  "log",
+ "lru",
  "nohash-hasher",
  "parity-scale-codec",
  "parking_lot 0.11.1",
@@ -9811,7 +9812,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "04f8ab788026715fa63b31960869617cba39117e520eb415b0139543e325ab59"
 dependencies = [
  "cfg-if 0.1.10",
- "rand 0.3.23",
+ "rand 0.7.3",
  "static_assertions",
 ]