Internal: Add LZF safe encoder in LZFCompressor

Selecting the safe encoder fixes a 64bit JVM crash on big-endian architectures with
LZF UnsafeChunkEncoderBE.

closes #7466
Revert part of change in #7466 to fix issue because encoder is not threadsafe so cannot be shared
Internal: Add all unsafe variants of LZF compress library functions to forbidden APIs.

The "optimized" encoders/decoders have been unreliable and error prone.
Also, fix LZFCompressor.compress to use LZFEncoder.safeEncode, which
creates a new safe encoder, instead of using a shared encoder (which
is not threadsafe).

closes #7468
[Test] testLargeClusterStatePublishing - bound max shard no to number of nodes and set replica count to 0

ensureGreen sometimes times out due to too many shards and GC kicking in
Parent/child: If _parent field points to a non existing parent type, then skip the has_parent query/filter

Closes #7362
Closes #7349
Parent/child: Add missing support for the field data loading option to the `_parent` field.

Closes #7394
Closes #7402
Mappings: Added support for empty field arrays

Close #7271
Use physical name to compare files from snapshot metadata

The comparison and read code in the BlobStoreIndexShardRepository
used the physicalName and Name in reverse order. This caused
SnapshotBackwardsCompatibilityTest to fail.

This reverts commit 636af40da1ae22d5b7c8a81435987768e9cc3ac9
Indexed Scripts : Change preference and thread option for GetRequest.

This change forces the GetRequest when a script is being loaded from an index
to use preference("_local") and threaded(false) to prevent the script service from
forking for GetRequests.
[TEST] removed AwaitsFix, added checks to make sure indexed scripts are put correctly
[TEST] only bump replicas if we have enough nodes in the cluster
Index templates: Made template filtering generic and extensible via plugins

Added the ability to register template filters that are being applied when a new index is created. The default filter that checks whether the template pattern matches the index name always runs first, additional filters can also be registered so that templates can be filtered out based on custom logic.

Took the chance to add the handy source(Object... source) method to PutIndexTemplateRequest and corresponding builder

Closes #7459
Closes #7454
explain score: fix explanation streaming

Complex explanations were always read as Explanations. Depending
on if the response was streamed or not the explanation was
therefore generated by a ComplexExplanation or by a regular
Explanation.

closes #7257
bool query: parser should return match_all in case there are no clauses

This also fixes has_parent filters with a nested empty bool filter
(see test SimpleChildQuerySearchTests#test6722, the test should actually expect
either 0 results when searching for has_parent "test" or one result when
search for has_parent "foo")

closes #7240
closes #7347
Fielddata: Remove soft/resident caches.

These caches have no advantage compared to the default node cache. Additionally,
the soft cache makes use of soft references which make fielddata loading quite
unpredictable in addition to pushing more pressure on the garbage collector.

The `none` cache is still there because of tests. There is no other good
reason to use it.

LongFieldDataBenchmark has been removed because the refactoring exposed a
compilation error in this class, which seems to not having been working for a
long time. In addition it's not as much useful now that we are progressively
moving more fields to doc values.

Close #7443
Add translog checksums

Switches TranslogStreams to check a header in the file to determine the
translog format, delegating to the version-specific stream.

Version 1 of the translog format writes a header using Lucene's
CodecUtil at the beginning of the file and appends a checksum for each
translog operation written.

Also refactors much of the translog operations, such as merging
.hasNext() and .next() in FsChannelSnapshot

Relates to #6554
Test: Allow global test cluster to have configurable settings source

This allows to reuse the global test cluster with specific configurations,
which is useful in plugins.
FunctionScore: Refactor RandomScoreFunction to be consistent, and return values in rang [0.0, 1.0]

RandomScoreFunction previously relied on the order the documents were
iterated in from Lucene. This caused changes in ordering, with the same
seed, if documents moved to different segments. With this change, a
murmur32 hash of the _uid for each document is used as the "random"
value. Also, the hash is adjusted so as to only return values between
0.0 and 1.0 to enable easier manipulation to fit into users' scoring
models.

closes #6907, #7446
[Tests] change BasicBackwardsCompatibilityTest to be compatible with 1.0.3

Also increase the time we wait for an external node to join
Sadly tests are not yet stable enough, testing with 1.0.3 is still disabled
[Internal] user node's cluster name as a default for an incoming cluster state who misses it

ClusterState has a reference to the cluster name since version 1.1.0 (df7474b9fcf849bbfea4222c1d2aa58b6669e52a) . However, if the state was  sent from a master of an older version, this name can be set to null. This is an unexpected and can cause bugs. The bad part is that it will never correct it self until a full cluster restart where the cluster state is rebuilt using the code of the latest version.

This commit changes the default to the node's cluster name.

Relates to #7386

Closes #7414