This change implements EIP-868. The UDPv4 transport announces support
for the extension in ping/pong and handles enrRequest messages.

There are two uses of the extension: If a remote node announces support
for EIP-868 in their pong, node revalidation pulls the node's record.
The Resolve method requests the record unconditionally.

These changes fix two corner cases related to internal handling of types
in package rlp: The "tail" struct tag can only be applied to the last field.
The check for this was wrong and didn't allow for private fields after the
field with the tag. Unsupported types (e.g. structs containing int) which
implement either the Encoder or Decoder interface but not both 
couldn't be encoded/decoded.

Also fixes #19367

cmd/faucet: remove Google+ mention from web assets too

* core, eth, trie: bloom filter for trie node dedup during fast sync

* eth/downloader, trie: address review comments

* core, ethdb, trie: restart fast-sync bloom construction now and again

* eth/downloader: initialize fast sync bloom on startup

* eth: reenable eth/62 until we properly remove it

* les, light: implement ODR transaction lookup by hash

* les: delete useless file

* internal/ethapi: always use backend to find transaction

* les, eth, internal/ethapi: renamed GetCanonicalTransaction to GetTransaction

* light: add canonical header verification to GetTransaction

p2p/discover: fix nil-dereference due to race

* move error variable to error.go

* Update error.go

Edit "Genesis" to "genesis"

* core: fix import errors on clique crashes + empty blocks

* cosensus/clique, core: add test for the mirrored state issue

* core: address todo question wrt log count

* core: raise a louder warning for non-clique known blocks

swarm v0.4-rc1

swarm/storage: remove traces for put/get/set (#1389)

* swarm/storage: remove traces for put/get/set

* swarm/storage: remove Has traces

swarm/storage/localstore: add gc metrics, disable flaky test

swarm/storage/localstore: fix broken metric (#1373)

p2p/protocols: count different messages (#1374)

cmd/swarm: disable snapshot create test due to constant flakes (#1376)

swarm/network: remove redundant goroutine (#1377)

swarm/network: add want delay timer to syncing (#1367)

swarm/network: synchronise peer.close() (#1369)

swarm/api: integrate tags to count chunks being split and stored
swarm/api/http: integrate tags in middleware for HTTP `POST` calls and assert chunks being calculated and counted correctly
swarm: remove deprecated and unused code, add swarm hash to DoneSplit signature, remove calls to the api client from the http package

* swarm/chunk: add tags backend to chunk package

swarm/network: measure how many chunks a node delivers (#1358)

* swarm/shed: remove metrics fields from DB struct

* swarm/schunk: add String methods to modes

* swarm/storage/localstore: add metrics and traces

* swarm/chunk: unknown modes without spaces in String methods

* swarm/storage/localstore: remove bin number from pull subscription metrics

* swarm/storage/localstore: add resetting time metrics and code improvements

cmd/swarm/swarm-smoke: improve smoke tests (#1337)

swarm/network: remove dead code (#1339)

swarm/network: remove FetchStore and SyncChunkStore in favor of NetStore (#1342)

 cmd/faucet: embed git commit hash/date, disable Google+

* add-date-to unstable

* fields-insteadof-split

* internal/build: support building with missing git

* docker: add git history back to support commit date in version

* internal/build: use PR commits hashes for PR builds

* core: import known blocks if they can be inserted as canonical blocks

* core: insert knowns blocks

* core: remove useless

* core: doesn't process head block in reorg function

eth/downloader: fix header delays during chain dedup