[INTERNAL] HasPopup enumeration lowercase transition
[INTERNAL] HasPopup enumeration lowercase transition

Until this change the values of sap.ui.core.aria.HasPopup were
returned with a capital first letter, requiring explicit toLowerCase
conversion. Most developers without some accessibility knowledge
would've used it incorrectly, generating BCP incidents afterwards.

Change-Id: I5a54ae48f55acb05e38a76f4a268becaf58362c6

SAP/openui5,SAP/openui5,SAP/openui5,SAP/openui5