Orca screen reader doesn't announce combobox value when focused

When a combobox is set as the buddy of a label, the currently selected option/value is not announced by the Orca screen reader when the combobox receives keyboard focus.

Sample steps to reproduce:

1. start the Orca screen reader
2. run the qtbase "contextinfo" sample (qtbase/examples/opengl/contextinfo/contextinfo)

1. move keyboard focus to the combobox using the tab key (move back and forth to retest) and notice that only "context version, combobox" is announced, but not the value/option that is currently selected
2. press Alt+Down_arrow to expand the popup holding the entries
3. move around and select another entry, e.g. "2.1", press Enter to confirm
4.  move focus back and forth again and notice that the proper value is announced now
5. switch value to "3.0" by just using the arrow down key, without opening the listbox popup. Note that this is not announced by the screen reader.
6. switch focus back and forth again and notice that the old value is announced: "context version, combobox, 2.1"

Observations and further notes:

• Orca just announces "context version, combobox", but not the current value when the popup hasn't been opened yet. The value should be announced right away.
• The value is announced when the combobox is not set as the buddy of a label. In that case, only the value of the combobox is announced, because the combobox uses the value as it's accessible name (s. QAccessibleComboBox::text).
• The wrong value is announced in step 8.
• orca version used: 45.0-1
• I plan to submit a suggested fix to Gerrit.

Expected result:

Orca should always announce the currently selected value/option as well, e.g. "context version, combobox, 2.0".