fix(ui5-notification-list): improve keyboard accessibility for the "More" button

[TeodorTaushanov]

Improve keyboard accessibility for the More button according to the specification.

• Single press of the 'Up Arrow' or 'Down Arrow' key shifts focus to the More button.
• Single press of the 'Home' key shifts focus to the first notification within the group.
• Single press of the 'End' key shifts focus to the last notification within the group. Double press of the 'End' key shifts focus to the More button within the group.

JIRA: BGSOFUIRODOPI-3215

[Stoev]

Please consider adding briefly what's included in the improvement (for example, which keys enable users to do smth).

Please double check whether the button's name corresponds to its name in the docu. At least in this sample, the button is called "More": https://sap.github.io/ui5-webcomponents/components/List/#growing-on-button-press

[TeodorTaushanov]

Please consider adding briefly what's included in the improvement (for example, which keys enable users to do smth).

Please double check whether the button's name corresponds to its name in the docu. At least in this sample, the button is called "More": https://sap.github.io/ui5-webcomponents/components/List/#growing-on-button-press

Done.

[Stoev]

Improve keyboard accessibility for the More button according to the specification.

• Single press of the 'Up Arrow' or 'Down Arrow' key shifts focus to the More button.
• Single press of the 'Home' key shifts focus to the first notification within the group.
• Single press of the 'End' key shifts focus to the last notification within the group. Double press of the 'End' key shifts focus to the More button within the group.

[TeodorTaushanov]

Improve keyboard accessibility for the More button according to the specification.

• Single press of the 'Up Arrow' or 'Down Arrow' key shifts focus to the More button.
• Single press of the 'Home' key shifts focus to the first notification within the group.
• Single press of the 'End' key shifts focus to the last notification within the group. Double press of the 'End' key shifts focus to the More button within the group.

Done

[Stoev]

Looks good to me.