Open issues page: Expand/ Collapse sidebar button is missing name and state.

Steps to reproduce:

1. Navigate to and activate "Projects" link from the banner region and select any project.
2. Navigate to and activate the "Issues" link from the left navigation menu.
3. With screen reader running navigate to the image button with tooltip "Expand/ collapse sidebar ( [ )"

Actual behaviour:

The Expand/ collapse sidebar ( [ ) button does not have an accessible name and therefore it is not announced for screen reader users when it receives keyboard focus.  Although currently the text is announced by the screen reader since aria-describedby attribute is provided but it is not the most efficient way to provide label to a button.

Expected result:

The button must have an accessible label via one of the following methods.

1. "aria-label" attribute : provide aria-label to the <button class='aui-sidebar-toggle'> element.

For Example : 

When sidebar is expanded then aria-label should be "Collapse sidebar [ "

When sidebar is Collapsed then aria-label should be "Expand sidebar [ "

2. Inner text: <button class='aui-sidebar-toggle'>Collapse sidebar [ </button> but the text should be off-screen.

3. aria-labelledby:

Provide an unique id to the <p> element & provide aria-labelledby attribute on <button> element. 

For Example

<button class="aui-sidebar-toggle" aria-labelledby="sidebartext">

<p class="aui-tooltip-content" id="sidebartext">Collapse sidebar ( [ )</p>

Remove the aria-describedby attribute from the <button> element as it would cause redundant announcement for screen reader users.

Screenshot:

AXQA Ref:AXQA-111