ESQL: Rename evaluators for FIRST and LAST (#132466)

I'm going to be reusing the evaluators from FIRST_OVER_TIME and
LAST_OVER_TIME for FIRST and LAST. This renames the evaluators
themselves to indicate that they are the actual evaluators for FIRST and
LAST.

Relates to #108385

Author: nik9000

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

@@ -900,28 +900,28 @@ tasks.named('stringTemplates').configure {
   }
 
   // TODO: add {value}_over_time for other types: boolean, bytes_refs
-  File valueOverTimeAggregatorInputFile = file("src/main/java/org/elasticsearch/compute/aggregation/X-ValueOverTimeAggregator.java.st")
+  File valueByTimestampAggregatorInputFile = file("src/main/java/org/elasticsearch/compute/aggregation/X-ValueByTimestampAggregator.java.st")
   ["First", "Last"].forEach { Occurrence ->
     {
       template {
         it.properties = addOccurrence(intProperties, Occurrence)
-        it.inputFile = valueOverTimeAggregatorInputFile
-        it.outputFile = "org/elasticsearch/compute/aggregation/${Occurrence}OverTimeIntAggregator.java"
+        it.inputFile = valueByTimestampAggregatorInputFile
+        it.outputFile = "org/elasticsearch/compute/aggregation/${Occurrence}IntByTimestampAggregator.java"
       }
       template {
         it.properties = addOccurrence(longProperties, Occurrence)
-        it.inputFile = valueOverTimeAggregatorInputFile
-        it.outputFile = "org/elasticsearch/compute/aggregation/${Occurrence}OverTimeLongAggregator.java"
+        it.inputFile = valueByTimestampAggregatorInputFile
+        it.outputFile = "org/elasticsearch/compute/aggregation/${Occurrence}LongByTimestampAggregator.java"
       }
       template {
         it.properties = addOccurrence(floatProperties, Occurrence)
-        it.inputFile = valueOverTimeAggregatorInputFile
-        it.outputFile = "org/elasticsearch/compute/aggregation/${Occurrence}OverTimeFloatAggregator.java"
+        it.inputFile = valueByTimestampAggregatorInputFile
+        it.outputFile = "org/elasticsearch/compute/aggregation/${Occurrence}FloatByTimestampAggregator.java"
       }
       template {
         it.properties = addOccurrence(doubleProperties, Occurrence)
-        it.inputFile = valueOverTimeAggregatorInputFile
-        it.outputFile = "org/elasticsearch/compute/aggregation/${Occurrence}OverTimeDoubleAggregator.java"
+        it.inputFile = valueByTimestampAggregatorInputFile
+        it.outputFile = "org/elasticsearch/compute/aggregation/${Occurrence}DoubleByTimestampAggregator.java"
       }
     }
   }