Fix layout when aggregating with aliases (elastic#117832)

Fix elastic#117770 Fix
elastic#117784

elastic#117699 made changes to how
we plan aggregations which were supposed to only trigger when a query
contained a `CATEGORIZE`, but accidentally changed a code path that
seems to only be required for interoperability with pre-8.13 nodes.
Because of this, we didn't notice failing tests until the periodic bwc
tests ran.

The code this PR fixes addresses situations where `Aggregate` plan nodes
contained _aliases inside the aggregates_. On `main` and `8.x`, this is
effectively an illegal state: since
elastic#104958, aliases in the
aggregates become `Eval` nodes before and after the `Aggregate` node.

But here, on 8.x, we'll just fix this code path so that it behaves
exactly as before elastic#117699.

If this passes the full-bwc test, I plan to forward-port this by
removing the obsolete code path on `main`.

x-pack/plugin/esql/qa/testFixtures/src/main/resources/stats.csv-spec

@@ -522,7 +522,7 @@ h:d  | languages:i
 1.41 | null
 ;
 
-groupByAlias#[skip:-8.13.99,reason:muted, see https://github.com/elastic/elasticsearch/issues/117770]
+groupByAlias
 from employees | rename languages as l | keep l, height | stats m = min(height) by l | sort l;
 
 m:d  | l:i
@@ -951,7 +951,7 @@ c:l
 49
 ;
 
-countFieldWithGrouping#[skip:-8.13.99,reason:muted, see https://github.com/elastic/elasticsearch/issues/117784]
+countFieldWithGrouping
 from employees | rename languages as l | where emp_no < 10050 | stats c = count(emp_no) by l | sort l;
 
 c:l | l:i 
@@ -963,7 +963,7 @@ c:l | l:i
 10 | null
 ;
 
-countFieldWithAliasWithGrouping#[skip:-8.13.99,reason:muted, see https://github.com/elastic/elasticsearch/issues/117784]
+countFieldWithAliasWithGrouping
 from employees | rename languages as l | eval e = emp_no | where emp_no < 10050 | stats c = count(e) by l | sort l;
 
 c:l | l:i 
@@ -982,7 +982,7 @@ c:l
 49  
 ;         
 
-countEvalExpWithGrouping#[skip:-8.13.99,reason:muted, see https://github.com/elastic/elasticsearch/issues/117784]
+countEvalExpWithGrouping
 from employees | rename languages as l | eval e = case(emp_no < 10050, emp_no, null) | stats c = count(e) by l | sort l;
 
 c:l | l:i 

x-pack/plugin/esql/qa/testFixtures/src/main/resources/version.csv-spec

@@ -159,7 +159,7 @@ id:i           |name:s         |version:v      |o:v
 13             |lllll          |null           |null 
 ;
 
-countVersion#[skip:-8.13.99,reason:muted, see https://github.com/elastic/elasticsearch/issues/117784]
+countVersion
 FROM apps | RENAME name AS k | STATS v = COUNT(version) BY k | SORT k;
 
 v:l     | k:s

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/planner/AbstractPhysicalOperationProviders.java

@@ -120,10 +120,14 @@ public final PhysicalOperation groupingPhysicalOperation(
                  *  - before stats (keep x = a | stats by x) which requires the partial input to use a's channel
                  *  - after  stats (stats by a | keep x = a) which causes the output layout to refer to the follow-up alias
                  */
+                // TODO: This is likely required only for pre-8.14 node compatibility; confirm and remove if possible.
+                // Since https://github.com/elastic/elasticsearch/pull/104958, it shouldn't be possible to have aliases in the aggregates
+                // which the groupings refer to. Except for `BY CATEGORIZE(field)`, which remains as alias in the grouping, all aliases
+                // should've become EVALs before or after the STATS.
                 for (NamedExpression agg : aggregates) {
                     if (agg instanceof Alias a) {
                         if (a.child() instanceof Attribute attr) {
-                            if (groupAttribute.id().equals(attr.id())) {
+                            if (sourceGroupAttribute.id().equals(attr.id())) {
                                 groupAttributeLayout.nameIds().add(a.id());
                                 // TODO: investigate whether a break could be used since it shouldn't be possible to have multiple
                                 // attributes pointing to the same attribute
@@ -133,8 +137,8 @@ public final PhysicalOperation groupingPhysicalOperation(
                             // is in the output form
                             // if the group points to an alias declared in the aggregate, use the alias child as source
                             else if (aggregatorMode.isOutputPartial()) {
-                                if (groupAttribute.semanticEquals(a.toAttribute())) {
-                                    groupAttribute = attr;
+                                if (sourceGroupAttribute.semanticEquals(a.toAttribute())) {
+                                    sourceGroupAttribute = attr;
                                     break;
                                 }
                             }