feat(ui5-list, ui5-tree): support accessible description

[dobrinyonkov]

Related to: #6445

Description

This PR adds support for the aria-describedby and the aria-description attribute to the ui5-list and ui5-tree components. These attributes allows developers to provide a reference to an element that describes the list or a string value, which can be read by screen readers.

Example

aria-description

A property accessibleDescription is added to the ui5-list and ui5-tree components. When set, the value of this property will be used as the accessible description of the list.

<ui5-list accessible-description="This is a list of items">...</ui5-list>

<ui5-tree accessible-description="This is a tree of items">...</ui5-tree>

aria-describedby

A property accessibleDescriptionRef is added to the ui5-list and ui5-tree components. When set, the value of this property will be used as the id of the element that describes the list.

<p id="description">This component has description</p>

<ui5-list accessible-description-ref="description">...</ui5-list>

<ui5-tree accessible-description-ref="description">...</ui5-tree>

Changes

• ui5-list and ui5-tree components now support the accessibleDescription and accessibleDescriptionRef properties
• An already existing utility named AriaLabelHelper was extended with a new methods getEffectiveAriaDescriptionText and getAllAccessibleDescriptionRefTexts to handle the new properties, similar to the ones for the aria-label attribute
• the name of the utility was changed to AccessibleTextsHelper to better reflect its purpose
• the ui5-list now subscribes for changes of the referenced elements using the AccessibleTextsHelper to update the aria-description and aria-label attribute of the list as well the
• ui5-tree only forwards the values to the internal ui5-tree-list which handles the property to attribute transformation

[ui5-webcomponents-bot]

🎉 This PR is included in version v2.5.0-rc.0 🎉

The release is available on v2.5.0-rc.0

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