[ES|QL] Auto open suggestions for field lists (#190466)

## Summary

Part of https://github.com/elastic/kibana/issues/189662

## Suggests comma and pipe


https://github.com/user-attachments/assets/c09bc6fd-20a6-4f42-a871-c70e68e6d81a

## Doesn't suggest comma when there are no more fields


https://github.com/user-attachments/assets/29fce13e-e58b-4d93-bce5-6b1f913b4d92

## Doesn't work for escaped columns :(


https://github.com/user-attachments/assets/3d65f3b9-923d-4c0e-9c50-51dd83115c8b

As part of this effort I discovered
https://github.com/elastic/kibana/issues/191100 and
https://github.com/elastic/kibana/issues/191105, as well as a problem
with column name validation (see
https://github.com/elastic/kibana/issues/177699)

I think we can revisit column escaping and probably resolve all of these
issues (issue [here](https://github.com/elastic/kibana/issues/191111)).


### Checklist

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

packages/kbn-esql-validation-autocomplete/scripts/generate_function_validation_tests.ts

@@ -23,6 +23,7 @@ import {
   dataTypes,
   fieldTypes,
   isFieldType,
+  FunctionParameter,
 } from '../src/definitions/types';
 import { FUNCTION_DESCRIBE_BLOCK_NAME } from '../src/validation/function_describe_block_name';
 import { getMaxMinNumberOfParams } from '../src/validation/helpers';
@@ -1155,7 +1156,7 @@ function generateIncorrectlyTypedParameters(
   signatures: FunctionDefinition['signatures'],
   currentParams: FunctionDefinition['signatures'][number]['params'],
   availableFields: Array<{ name: string; type: SupportedDataType }>
-) {
+): { wrongFieldMapping: FunctionParameter[]; expectedErrors: string[] } {
   const literalValues = {
     string: `"a"`,
     number: '5',
@@ -1260,7 +1261,7 @@ function generateIncorrectlyTypedParameters(
     })
     .filter(nonNullable);
 
-  return { wrongFieldMapping, expectedErrors };
+  return { wrongFieldMapping: wrongFieldMapping as FunctionParameter[], expectedErrors };
 }
 
 /**