…ic#110652)

A query like:

```
FROM sample_data, sample_data_str
| STATS count=count(*) BY client_ip = TO_IP(client_ip)
| SORT count DESC, client_ip ASC
| KEEP count, client_ip
```

Failed due to unresolved aggregates from the union-type in the grouping key

* Fix bug in union-types with type-casting in grouping key of STATS (#110476)

* Allow auto-generated type-cast fields in CsvTests

This allows, for example, a csv-spec test result header like `client_ip::ip:ip`, which is generated with a command like `STATS count=count(*) BY client_ip::ip`

It is also a small cleanup of the header parsing code, since it was using Strings.split() in an odd way.

* Fix bug in union-types with type-casting in grouping key of STATS

* Update docs/changelog/110476.yaml

* Added casting_operator required capability

Using the new `::` syntax requires disabling support for older versions in multi-cluster tests.

* Added more tests for inline stats over long/datetime

* Trying to fix the STATS...STATS bug

This makes two changes:

* Keeps the Alias in the aggs.aggregates from the grouping key, so that ReplaceStatsNestedExpressionWithEval still works
* Adds explicit support for union-types conversion at grouping key loading in the ordinalGroupingOperatorFactory

Neither fix the particular edge case, but do seem correct

* Added EsqlCapability for this change

So that mixed cluster tests don't fail these new queries.

* Fix InsertFieldExtract for union types

Union types require a FieldExtractExec to be performed first thing at
the bottom of local physical plans.

In queries like
```
  from testidx*
  | eval x = to_string(client_ip)
  | stats c = count(*) by x
  | keep c
```
The `stats` has the grouping `x` but the aggregates get pruned to just
`c`. In cases like this, we did not insert a FieldExtractExec, which
this fixes.

* Revert query that previously failed

With Alex's fix, this query now passes.

* Revert integration of union-types to ordinals aggregator

This is because we have not found a test case that actually demonstrates this is necessary.

* More tests that would fail without the latest fix

* Correct code style

* Fix failing case when aggregating on union-type with invalid grouping key

* Capabilities restrictions on the new YML tests

* Update docs/changelog/110476.yaml

---------

Co-authored-by: Alexander Spies <alexander.spies@elastic.co>

* An alternative approach to supporting union-types on stats grouping field (#110600)

* Added union-types field extration to ordinals aggregation

* Revert previous approach to getting union-types working in aggregations

Where the grouping field is erased by later commands, like a subsequent stats.
Instead we include union-type supports in the ordinals aggregation and mark the block loader as not supporting ordinals.

* Fix union-types when aggregating on inline conversion function (#110652)

A query like:

```
FROM sample_data, sample_data_str
| STATS count=count(*) BY client_ip = TO_IP(client_ip)
| SORT count DESC, client_ip ASC
| KEEP count, client_ip
```

Failed due to unresolved aggregates from the union-type in the grouping key

* Fix for union-types for multiple columns with the same name (#110793)

* Make union types use unique attribute names

* Cleanup leftover

* Added failing test and final fix to EsRelation

* Implement FieldAttribute.fieldName()

* Fix tests

* Refactor

* Do not ignore union typed field's parent

* Fix important typo

D'oh

* Mute unrelated (part of) test

* Move capability to better location

* Fix analyzer tests

* multi-node tests with an earlier version of union-types (before this change) fail

* Add capability to remaining failing tests

* Remove variable

* Add more complex test

* Consolidate union type cleanup rules

* Add 3 more required_capability's to make CI happy

* Update caps for union type subfield yaml tests

* Update docs/changelog/110793.yaml

* Refined changelog text

* Mute BWC for 8.15.0 for failing YAML tests

* union_types_remove_fields for all 160_union_types tests

The tests fail spordically, so safer to mute the entire suite.

---------

Co-authored-by: Alexander Spies <alexander.spies@elastic.co>

---------

Co-authored-by: Alexander Spies <alexander.spies@elastic.co>

A query like:

```
FROM sample_data, sample_data_str
| STATS count=count(*) BY client_ip = TO_IP(client_ip)
| SORT count DESC, client_ip ASC
| KEEP count, client_ip
```

Failed due to unresolved aggregates from the union-type in the grouping key

A query like:

```
FROM sample_data, sample_data_str
| STATS count=count(*) BY client_ip = TO_IP(client_ip)
| SORT count DESC, client_ip ASC
| KEEP count, client_ip
```

Failed due to unresolved aggregates from the union-type in the grouping key