[data.search.aggs]: Create agg types function for terms agg. (#63541)

* Minor cleanup on AggConfigJson interface.

* Add types for terms agg params & mapping.

* Add terms agg expression function.

* Register agg functions with expressions service.

* Add unit tests for terms expression function.

* Update API docs.

* AggConfigJson -> AggConfigSerialized

* Add serialize(), enforce serializable params, fix subexpressions in terms agg fn.

* Simplify getAggTypesFunctions

* it() -> test()

* Add help text.

* Ensure serialize() is used by agg param type.

* Add toExpressionAst to AggConfig.

* Add json arg to terms agg fn.

* Update docs.

* Fix typo which caused functional test failures.

* Add AggParam.toExpressionAst so AggConfig.toExpressionAst can return function ast instead of expression ast.

* Clean up overlooked items.

Author: lukeelmers

docs/development/plugins/data/public/kibana-plugin-plugins-data-public.aggconfigoptions.enabled.md

@@ -2,21 +2,12 @@
 
 [Home](./index.md) > [kibana-plugin-plugins-data-public](./kibana-plugin-plugins-data-public.md) > [AggConfigOptions](./kibana-plugin-plugins-data-public.aggconfigoptions.md)
 
-## AggConfigOptions interface
+## AggConfigOptions type
 
 <b>Signature:</b>
 
 ```typescript
-export interface AggConfigOptions 
+export declare type AggConfigOptions = Assign<AggConfigSerialized, {
+    type: IAggType;
+}>;
 ```
-
-## Properties
-
-|  Property | Type | Description |
-|  --- | --- | --- |
-|  [enabled](./kibana-plugin-plugins-data-public.aggconfigoptions.enabled.md) | <code>boolean</code> |  |
-|  [id](./kibana-plugin-plugins-data-public.aggconfigoptions.id.md) | <code>string</code> |  |
-|  [params](./kibana-plugin-plugins-data-public.aggconfigoptions.params.md) | <code>Record&lt;string, any&gt;</code> |  |
-|  [schema](./kibana-plugin-plugins-data-public.aggconfigoptions.schema.md) | <code>string</code> |  |
-|  [type](./kibana-plugin-plugins-data-public.aggconfigoptions.type.md) | <code>IAggType</code> |  |
-

docs/development/plugins/data/public/kibana-plugin-plugins-data-public.aggconfigoptions.id.md

@@ -7,5 +7,5 @@
 <b>Signature:</b>
 
 ```typescript
-makeAgg: (agg: TAggConfig, state?: any) => TAggConfig;
+makeAgg: (agg: TAggConfig, state?: AggConfigSerialized) => TAggConfig;
 ```

docs/development/plugins/data/public/kibana-plugin-plugins-data-public.aggconfigoptions.md

@@ -21,5 +21,5 @@ export declare class AggParamType<TAggConfig extends IAggConfig = IAggConfig> ex
 |  Property | Modifiers | Type | Description |
 |  --- | --- | --- | --- |
 |  [allowedAggs](./kibana-plugin-plugins-data-public.aggparamtype.allowedaggs.md) |  | <code>string[]</code> |  |
-|  [makeAgg](./kibana-plugin-plugins-data-public.aggparamtype.makeagg.md) |  | <code>(agg: TAggConfig, state?: any) =&gt; TAggConfig</code> |  |
+|  [makeAgg](./kibana-plugin-plugins-data-public.aggparamtype.makeagg.md) |  | <code>(agg: TAggConfig, state?: AggConfigSerialized) =&gt; TAggConfig</code> |  |
 

docs/development/plugins/data/public/kibana-plugin-plugins-data-public.aggconfigoptions.params.md

@@ -49,7 +49,6 @@
 
 |  Interface | Description |
 |  --- | --- |
-|  [AggConfigOptions](./kibana-plugin-plugins-data-public.aggconfigoptions.md) |  |
 |  [AggParamOption](./kibana-plugin-plugins-data-public.aggparamoption.md) |  |
 |  [DataPublicPluginSetup](./kibana-plugin-plugins-data-public.datapublicpluginsetup.md) |  |
 |  [DataPublicPluginStart](./kibana-plugin-plugins-data-public.datapublicpluginstart.md) |  |
@@ -118,6 +117,7 @@
 
 |  Type Alias | Description |
 |  --- | --- |
+|  [AggConfigOptions](./kibana-plugin-plugins-data-public.aggconfigoptions.md) |  |
 |  [AggParam](./kibana-plugin-plugins-data-public.aggparam.md) |  |
 |  [CustomFilter](./kibana-plugin-plugins-data-public.customfilter.md) |  |
 |  [EsQuerySortValue](./kibana-plugin-plugins-data-public.esquerysortvalue.md) |  |

docs/development/plugins/data/public/kibana-plugin-plugins-data-public.aggconfigoptions.schema.md

@@ -139,6 +139,7 @@ export class DataPublicPlugin implements Plugin<DataPublicPluginSetup, DataPubli
     return {
       autocomplete: this.autocomplete.setup(core),
       search: this.searchService.setup(core, {
+        expressions,
         getInternalStartServices,
         packageInfo: this.packageInfo,
         query: queryService,