user32/tests: Add message tests for EM_SETSEL when getting/losing focus in combo boxes

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://testbot.winehq.org/JobDetails.pl?Key=19318

Your paranoid android.


=== wvistau64 (32 bit msg) ===
msg.c:10877: Test failed: expected PeekMessage to return FALSE, got 1
msg.c:10889: Test failed: msg.message = 275 instead of WM_USER
msg.c:10891: Test failed: expected PeekMessage to return FALSE, got 1
msg.c:10900: Test failed: msg.message = 1024 instead of WM_TIMER
msg.c:10902: Test failed: expected PeekMessage to return FALSE, got 1
msg.c:13824: Test failed: 0: WaitForSingleObject failed

=== w1064 (32 bit msg) ===
msg.c:6290: Test failed: Update region shouldn't be empty
msg.c:6524: Test failed: InvalidateErase: 0: the msg sequence is not complete: expected 0085 - actual 0000
msg.c:6526: Test failed: Paint: 0: the msg sequence is not complete: expected 000f - actual 0000
msg.c:6296: Test failed: Regions are different
msg.c:6296: Test failed: Regions are different
msg.c:6296: Test failed: Regions are different