Combobox keyboard search should match multiple letters

(This ticket is kind of a follow-up to CORE-16376.)

Steps:
1. Open 'Control Panel' > 'Regional and Language Options'.
2. Open 'Location' dropdown.
3. Type 'f' then 'r'.
3r.
WXP: 'France' is selected.
ROS: uses 'r' as a new search.

Note:

• After a short delay, typing another letter should start a new search.
• Typing 'f' multiple times does cycle through 'f...' entries, as expected.

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This looks like
https://bugs.winehq.org/show_bug.cgi?id=42898