Combobox examples with both and list autocomplete: Add regression tests for Backspace

[mcking65]

Prevent regression of backspace behaviors from bug #1332 in:

1. autocomplete = both example
2. autocomplete = list example

Implement the following tests in Ava.

Test 1

1. Load the combobox with autocomplete = both example
2. Focus the combobox and type "a".
3. Type backspace to delete the auto-highlighted text "labama"
4. Press backspace to delete the "a".
5. Press down arrow.

Expected result: There are 56 suggested values in the listbox and "Alabama" is selected.

Test 2

1. Load the combobox with autocomplete = both example
2. Focus the combobox and type "no".
3. Press Backspace to delete the auto-highlighted text "rth Carolina"
4. Press backspace to delete the "o".
5. Press down arrow.

Expected result: There are 9 suggested values in the listbox and "Nebraska" is selected.

Test 3

1. Load the combobox with list autocomplete example.
2. Focus the combobox and type "a".
3. Press backspace to delete the "a".
4. Press down arrow.

Expected result: There are 56 suggested values in the listbox and "Alabama" is selected.

Test 4

1. Load the combobox with list autocomplete example.
2. Focus the combobox and type "no".
3. Press backspace to delete the "o".
4. Press down arrow.

Expected result: There are 9 suggested values in the listbox and "Nebraska" is selected.