Rename prepareProcessPage to prepareProcessRawInputPage (elastic#130487)

This PR proposes renaming `prepareProcessPage` to
`prepareProcessRawInputPage` for two reasons:

1. The name `prepareProcessPage` can be confusing, as it suggests
handling all types of input, but it only processes raw input, not
intermediate input.

2. I plan to add `prepareProcessIntermediateInputPage`, which can enable
optimizations for intermediate pages, such as leveraging ordinals from
intermediate results.

(cherry picked from commit 285866e)

Author: dnhatn

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

@@ -195,7 +195,7 @@ private TypeSpec type() {
         builder.addMethod(ctor());
         builder.addMethod(intermediateStateDesc());
         builder.addMethod(intermediateBlockCount());
-        builder.addMethod(prepareProcessPage());
+        builder.addMethod(prepareProcessRawInputPage());
         builder.addMethod(addRawInputLoop(INT_VECTOR, blockType(aggParam.type())));
         builder.addMethod(addRawInputLoop(INT_VECTOR, vectorType(aggParam.type())));
         builder.addMethod(addRawInputLoop(INT_BLOCK, blockType(aggParam.type())));
@@ -310,10 +310,10 @@ private MethodSpec intermediateBlockCount() {
     }
 
     /**
-     * Prepare to process a single page of results.
+     * Prepare to process a single raw input page.
      */
-    private MethodSpec prepareProcessPage() {
-        MethodSpec.Builder builder = MethodSpec.methodBuilder("prepareProcessPage");
+    private MethodSpec prepareProcessRawInputPage() {
+        MethodSpec.Builder builder = MethodSpec.methodBuilder("prepareProcessRawInputPage");
         builder.addAnnotation(Override.class).addModifiers(Modifier.PUBLIC).returns(GROUPING_AGGREGATOR_FUNCTION_ADD_INPUT);
         builder.addParameter(SEEN_GROUP_IDS, "seenGroupIds").addParameter(PAGE, "page");