Implementation of Delta function for absolute change in gauges over time (#135035)

* Implementation of Delta function for absolute change in gauges over time window

* csv tests

* fixup

* add extrapolation code for Delta

* fixup

* fixup

* fxup

* foxup

* fix csv tests

Author: pabloem

x-pack/plugin/esql/compute/build.gradle

@@ -513,6 +513,28 @@ tasks.named('stringTemplates').configure {
     it.outputFile = "org/elasticsearch/compute/aggregation/IrateDoubleAggregator.java"
   }
 
+  File deltaAggregatorInputFile = file("src/main/java/org/elasticsearch/compute/aggregation/X-DeltaAggregator.java.st")
+  template {
+    it.properties = intProperties
+    it.inputFile = deltaAggregatorInputFile
+    it.outputFile = "org/elasticsearch/compute/aggregation/DeltaIntAggregator.java"
+  }
+  template {
+    it.properties = longProperties
+    it.inputFile = deltaAggregatorInputFile
+    it.outputFile = "org/elasticsearch/compute/aggregation/DeltaLongAggregator.java"
+  }
+  template {
+    it.properties = floatProperties
+    it.inputFile = deltaAggregatorInputFile
+    it.outputFile = "org/elasticsearch/compute/aggregation/DeltaFloatAggregator.java"
+  }
+  template {
+    it.properties = doubleProperties
+    it.inputFile = deltaAggregatorInputFile
+    it.outputFile = "org/elasticsearch/compute/aggregation/DeltaDoubleAggregator.java"
+  }
+
   File fallibleStateInputFile = new File("${projectDir}/src/main/java/org/elasticsearch/compute/aggregation/X-FallibleState.java.st")
   template {
     it.properties = booleanProperties