ESQL: Unmute test and reuse blockFactory to avoid concurrently modifying the test factories list (#128211) (#128243)

Fixes #128092

The error happens inside an ArrayList.add(), and it's a concurrency-related one.

The stacktrace is quite explicative:
```
java.lang.ArrayIndexOutOfBoundsException: Index 34 out of bounds for length 33
at java.util.ArrayList.add(ArrayList.java:485)
at org.elasticsearch.compute.test.ComputeTestCase.blockFactory(ComputeTestCase.java:62)
at org.elasticsearch.compute.aggregation.GroupingAggregatorFunctionTestCase$4$1$1.addBlock(GroupingAggregatorFunctionTestCase.java:659)
```

We were creating new blockFactories() inside the aggregator, which was being called concurrently with different drivers. As `blockFactory()` adds it to a static ArrayList, it was sometimes throwing.

The bug only affects tests. Potentially, all grouping aggregators tests.

Author: ivancea

x-pack/plugin/esql/compute/src/test/java/org/elasticsearch/compute/aggregation/GroupingAggregatorFunctionTestCase.java

@@ -651,7 +651,7 @@ public AddInput prepareProcessPage(SeenGroupIds ignoredSeenGroupIds, Page page)
                             @Override
                             public void add(int positionOffset, IntBlock groupIds) {
                                 for (int offset = 0; offset < groupIds.getPositionCount(); offset += emitChunkSize) {
-                                    try (IntBlock.Builder builder = blockFactory().newIntBlockBuilder(emitChunkSize)) {
+                                    try (IntBlock.Builder builder = driverContext.blockFactory().newIntBlockBuilder(emitChunkSize)) {
                                         int endP = Math.min(groupIds.getPositionCount(), offset + emitChunkSize);
                                         for (int p = offset; p < endP; p++) {
                                             int start = groupIds.getFirstValueIndex(p);