[8.19] Backport ES|QL sample agg function (#129627)

* ES|QL SAMPLE aggregation function (#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]>

* Fix + unmute SampleTests (#127959)

* Fix memory tracking of ES|QL sample agg (#128467)

* Fix memory tracking of ES|QL sample agg

* [CI] Auto commit changes from spotless

* polish code

---------

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

* ESQL: Unclean generated imports (#127723)

This removes a ton of the tricky juggling we do for generated java files
to keep the imports in order. Instead, we just live with them being out
of order a little. It's not great, but it's so so so much easier than
the terrible juggling we had been doing.

* ESQL: Disable format checks on generated imports (#127648)

This builds the infrastructure to disable spotless and some checkstyle
rules on generated imports. This works around the most frustrating part
of ESQL's string template generated files - the imports. It allows
unused and out of order imports. This can let us remove a lot of
cumbersome, tricky, and fairly useless `$if$` blocks from the templates.

---------

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

Author: 3 people

build-tools-internal/src/main/resources/checkstyle.xml

@@ -68,6 +68,11 @@
 
     <!-- Unused imports are forbidden -->
     <module name="UnusedImports" />
+    <module name="SuppressionCommentFilter">
+      <property name="offCommentFormat" value="begin generated imports"/>
+      <property name="onCommentFormat" value="end generated imports"/>
+      <property name="checkFormat" value="UnusedImports"/>
+    </module>
 
     <!-- Non-inner classes must be in files that match their names. -->
     <module name="OuterTypeFilename" />

docs/changelog/127629.yaml

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