[INTERNAL] sap.m.ComboBox: Add .sapMComboBoxFocused CSS class when is focused.

Add the specified class when focusin is fired on the ComboBox and then
remove the class when sapfocusleave events is fired

Change-Id: I5d5b7ebc7b97c6c9276c3ddbf4fe411b5535bb71
Merge "[INTERNAL] sap.m.ComboBox: Add .sapMComboBoxFocused CSS class when is focused."