ESQL: Support for multi-argument aggs (#132424)

Adds support for multi-argument grouped aggs. Previously we only had
support for aggs with a value and a timestamp. Now we can support any
number of fields.

This change is mostly mechanical and mostly in generated code. The only
production code changes are:
1. Rename things like `block` and `vector` to `fooBlock` so names are
   unique with multi-argument fields. `foo` comes from the name of the
   argument to `combine`.
2. Support for passing `Block`s of `long`s in `FirstOverTime` and
   `LastOverTime`. This will allow it to function outside of TSDB.
3. Flip the order of the arguments in the `combine` methods for
   `FirstOverTime` and `LastOverTime` so they line up with how the ESQL
   code orders the arguments. This shouldn't change the runtime at all.
4. Rename the offset variable we use for reading from vectors in
   non-grouped code so it's the same name as we use in grouped code.
   This just keeps the code gen a little more consistent.

Author: nik9000

x-pack/plugin/esql/compute/gen/src/main/java/org/elasticsearch/compute/gen/AggregatorImplementer.java

@@ -106,7 +106,6 @@ public AggregatorImplementer(
             requireName("combine"),
             requireArgsStartsWith(requireType(aggState.declaredType()), requireAnyType("<aggregation input column type>"))
         );
-
         this.aggParams = combine.getParameters().stream().skip(1).map(AggregationParameter::create).toList();
 
         this.createParameters = init.getParameters()
@@ -344,10 +343,13 @@ private MethodSpec addRawVector(boolean masked) {
             builder.addStatement("state.seen(true)");
         }
 
-        builder.beginControlFlow("for (int i = 0; i < $L.getPositionCount(); i++)", aggParams.getFirst().vectorName());
+        builder.beginControlFlow(
+            "for (int valuesPosition = 0; valuesPosition < $L.getPositionCount(); valuesPosition++)",
+            aggParams.getFirst().vectorName()
+        );
         {
             if (masked) {
-                builder.beginControlFlow("if (mask.getBoolean(i) == false)").addStatement("continue").endControlFlow();
+                builder.beginControlFlow("if (mask.getBoolean(valuesPosition) == false)").addStatement("continue").endControlFlow();
             }
             for (AggregationParameter p : aggParams) {
                 p.read(builder, true);
@@ -420,11 +422,14 @@ private MethodSpec addRawBlock(boolean masked) {
         return builder.build();
     }
 
-    private MethodSpec.Builder initAddRaw(boolean isVector, boolean masked) {
-        MethodSpec.Builder builder = MethodSpec.methodBuilder(isVector ? "addRawVector" : "addRawBlock");
+    private MethodSpec.Builder initAddRaw(boolean valuesAreVector, boolean masked) {
+        MethodSpec.Builder builder = MethodSpec.methodBuilder(valuesAreVector ? "addRawVector" : "addRawBlock");
         builder.addModifiers(Modifier.PRIVATE);
         for (AggregationParameter p : aggParams) {
-            builder.addParameter(isVector ? vectorType(p.type) : blockType(p.type), isVector ? p.vectorName() : p.blockName());
+            builder.addParameter(
+                valuesAreVector ? vectorType(p.type) : blockType(p.type),
+                valuesAreVector ? p.vectorName() : p.blockName()
+            );
         }
         if (masked) {
             builder.addParameter(BOOLEAN_VECTOR, "mask");
@@ -440,7 +445,7 @@ private MethodSpec.Builder initAddRaw(boolean isVector, boolean masked) {
 
     private void combineRawInput(MethodSpec.Builder builder) {
         TypeName returnType = TypeName.get(combine.getReturnType());
-        warningsBlock(builder, () -> { invokeCombineRawInput(returnType, builder); });
+        warningsBlock(builder, () -> invokeCombineRawInput(returnType, builder));
     }
 
     private void invokeCombineRawInput(TypeName returnType, MethodSpec.Builder builder) {
@@ -451,9 +456,11 @@ private void invokeCombineRawInput(TypeName returnType, MethodSpec.Builder build
             params.add(returnType);
             params.add(declarationType);
             params.add(returnType);
-        } else {
+        } else if (returnType == TypeName.VOID) {
             pattern.append("$T.combine(state");
             params.add(declarationType);
+        } else {
+            throw new IllegalArgumentException("combine must return void or a primitive");
         }
         for (AggregationParameter p : aggParams) {
             pattern.append(", $L");
@@ -753,7 +760,7 @@ public void read(MethodSpec.Builder builder, boolean vector) {
             params.add(vector ? vectorName() : blockName());
             params.add(readMethod());
             if (vector) {
-                pattern.append("i");
+                pattern.append("valuesPosition");
             } else {
                 pattern.append("$L");
                 params.add(offsetName());