Always prefer text events by default

This improves text input, but it breaks the expected behavior in games
again: <https://github.com/Genymobile/scrcpy/issues/87>.

To get the previous behavior back, pass an explicit option:

    scrcpy --prefer-text-events=non-alpha

app/scrcpy.1

@@ -69,7 +69,7 @@ Possible \fImode\fRs are "always" (every text is sent as text), "non-alpha"
 (only letters are sent as a sequence of key events, other characters are sent
 as text) and "never" (every text is sent as a sequence of key events).
 
-Default is "non-alpha".
+Default is "always".
 
 .TP
 .BI "\-\-push\-target " path