[MM-20979] Add first implementation of the Bleve search engine (#14562)

* [MM-20979] Add first implementation of the Bleve search engine

* Fix i18n

* Migrate searchengine utils tests

* Fix linter

* Don't add allTermsQ if both termQueries and notTermQueries are empty

* Fix test that should work if user is system admin

* Modify naming according to review comments

* Abstract getIndexDir function

* Extracting bleve engine name as a constant

* Merge both Indexer interfaces into one

* Add worker stopped message

* Allow worker to be started/stopped with config change

* Use constants for index names

* Modify test order

* Fix linter

* Trying to unlock the CI

vendor/github.com/RoaringBitmap/roaring/popcnt_compat.go

@@ -0,0 +1,17 @@
+// +build !go1.9
+
+package roaring
+
+// bit population count, take from
+// https://code.google.com/p/go/issues/detail?id=4988#c11
+// credit: https://code.google.com/u/arnehormann/
+// credit: https://play.golang.org/p/U7SogJ7psJ
+// credit: http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
+func popcount(x uint64) uint64 {
+	x -= (x >> 1) & 0x5555555555555555
+	x = (x>>2)&0x3333333333333333 + x&0x3333333333333333
+	x += x >> 4
+	x &= 0x0f0f0f0f0f0f0f0f
+	x *= 0x0101010101010101
+	return x >> 56
+}