[RAC] [TGrid] Implements sorting in the TGrid

This PR implements sorting in the `TGrid`, per the animated gifs below:

![observability-sorting](https://user-images.githubusercontent.com/4459398/127960825-5be21a92-81c1-487d-9c62-1335495f4561.gif)

_Above: Sorting in Observability, via `EuiDataGrid`'s sort popover_

![security-solution-sorting](https://user-images.githubusercontent.com/4459398/127961574-00639d4d-762c-4529-bc43-6851d98728da.gif)

_Above: Sorting and hiding columns in the Security Solution via `EuiDataGrid`'s column header actions_

* Sorting is disabled for non-aggregatble fields
* This PR resolves the `Sort [Object Object]` TODO described [here](elastic#106199 (comment))
* This PR restores the column header tooltips where the TGrid is used in the Security Solution

* The `Hide column` action now hides the selected column. Users may re-add hidden columns via the `Fields` browser

@mdefazio, please note this behavior differs slightly from the following request in elastic#106585 :

> Include toggles on column modifier popover to allow for show/hide option (And the field menu would only be for what is available in the column list) See [EUI Docs examples](https://elastic.github.io/eui/#/tabular-content/data-grid) for expected behavior

The behavior is different because, if the `Hide column` action only interacted with the toggles in the column modifier popover, users would have to (re) locate the field in the `Fields` browser, and then uncheck it, to _actually_ remove the column.

To allow users to remove columns in a single step, and to avoid confusion, toggles are **not** included in the column modifier popover.

To desk test this PR, you must enable feature flags in the Observability and Security Solution:

- To desk test the `Observability > Alerts` page, add the following settings to `config/kibana.dev.yml`:

```
xpack.observability.unsafe.cases.enabled: true
xpack.observability.unsafe.alertingExperience.enabled: true
xpack.ruleRegistry.write.enabled: true
```

- To desk test the TGrid in the following Security Solution, edit `x-pack/plugins/security_solution/common/experimental_features.ts` and in the `allowedExperimentalValues` section set:

```typescript
tGridEnabled: true,
``

cc @mdefazio

x-pack/plugins/timelines/common/types/timeline/columns/index.ts

@@ -17,7 +17,13 @@ export type ColumnId = string;
 /** The specification of a column header */
 export type ColumnHeaderOptions = Pick<
   EuiDataGridColumn,
-  'display' | 'displayAsText' | 'id' | 'initialWidth'
+  | 'actions'
+  | 'defaultSortDirection'
+  | 'display'
+  | 'displayAsText'
+  | 'id'
+  | 'initialWidth'
+  | 'isSortable'
 > & {
   aggregatable?: boolean;
   category?: string;