ES|QL SAMPLE aggregation function (elastic#127629)

* ES|QL SAMPLE aggregation function

* [CI] Auto commit changes from spotless

* ThreadLocalRandom -> SplittableRandom

* Update docs/changelog/127629.yaml

* fix yaml test

* Add SampleTests

* docs + example

* polish code

* mark generated imports

* comment with algorith description

* use Randomness.get()

* close properly

* type checks

* reuse hash

* regen some files

* [CI] Auto commit changes from spotless

---------

Co-authored-by: elasticsearchmachine <[email protected]>

Author: jan-elastic

docs/changelog/127629.yaml

@@ -0,0 +1,5 @@
+pr: 127629
+summary: ES|QL SAMPLE aggregation function
+area: Machine Learning
+type: feature
+issues: []

docs/reference/query-languages/esql/_snippets/functions/description/sample.md

@@ -81,7 +81,7 @@ static class IntermediateResult {
     private static long C1 = 0x87c37b91114253d5L;
     private static long C2 = 0x4cf5ad432745937fL;
 
-    protected static long fmix(long k) {
+    public static long fmix(long k) {
         k ^= k >>> 33;
         k *= 0xff51afd7ed558ccdL;
         k ^= k >>> 33;