fix(data-tables): Add missing release notes and tests (#4678)

* fix and update data tables release notes

* add data table test to capture sorted header markup

* add a11y note in docs about `aria-live` for search stickiness

Author: Dottenpixel

RELEASENOTES.md

@@ -21,13 +21,22 @@
 
 ## Release 2.15.2 - April 13, 2021
 
+## Components
+### [Data Tables](https://www.lightningdesignsystem.com/components/data-tables)
+#### Added
+- Added `aria-label`, and alternatively, `aria-labelledby` to allow adding additional table context for screen readers
+
 ## Release 2.15.1 - April 12, 2021
 
 ## Components
 ### [Cards](https://www.lightningdesignsystem.com/components/cards)
 #### Added
 - Added annotations for Einstein themed cards
 
+### [Data Tables](https://www.lightningdesignsystem.com/components/data-tables)
+#### Changed
+- Changed the `aria-live` value from `assertive` to `polite`
+
 ### [Menus](https://www.lightningdesignsystem.com/components/menus)
 #### Added
 - Added `aria-expanded` attribute to menu triggers with value dependent on menu's open state
@@ -198,6 +207,10 @@ Refactored the component markup to function with or without theme utility classe
 #### Added
 - Enabled styling hooks for checkbox toggle. See checkbox toggle's styling hooks overview table for a full listing of the currently available hooks.
 
+### [Data Tables](https://www.lightningdesignsystem.com/components/data-tables)
+#### Added
+- Added `slds-cell_action-mode` class for styling cells in Action mode
+
 ### [Form Element](https://www.lightningdesignsystem.com/components/form-element)
 #### Fixed
 - Adjusted space between the form label and the information button icon for Mobile.

ui/components/data-tables/RELEASENOTES.md

@@ -4,10 +4,19 @@
 
 <!-- ## [Unreleased] -->
 
-# 2.15.2
+## 2.15.2
+
+### Added
 
 - Added `aria-label`, and alternatively, `aria-labelledby` to allow adding additional table context for screen readers
-# 2.14.0
+
+## 2.15.1
+
+### Changed
+
+- Changed the `aria-live` value from `assertive` to `polite`
+
+## 2.14.0
 
 ### Added