Handle font style on loading default Terminal preferences

Fix the PrefHandler::_ConfirmFont to take into account not only the
font family but the font style too. This improves the popup menu
checkmark synchronization in the Preferences View. This problem can
be reproduced on very first start of application without previously
stored Terminal settings. Default family/style for this case is
currently defined as "Courier 19BT"/"Regular" but default fixed
font has correspondently "DejaVu Sans Mono"/"Book". Previous version
of _ConfirmFont() process only the family and left the style in default
"Regular" one. So opening Preferences View and attempting to set the
checkmark on corresponding family/style menuitem was usually failed.
Omit Terminal Id title in case single app instance running

Hide the current index of Terminal window from it's title if only
ony instance of the Terminal application is running in the system.

Fixes #9530.
Fix Terminal cursor Save/Restore behaviour

Yet another fix for the terminal cursor save/restore functionality.
Fixes wrong cursor positions observed in modern versions of the
Midnight Commander during switching between Alternate and Normal buffers.
Terminal data flow debug capture improved

This modification moves the debug characters capture call directly into
the _NextParseChar(). That allows to capture all data flow without
missing things like OSC control sequences.
Fix Alternate/Normal screen's current attributes handling

Handle the current attributes of the TextBuffer consistently with other
Alt/Normal buffer sensitive variables. That fixes, for example, issues
with wrong background coloring of new lines in normal text buffer after
maximizing the terminal window running applications (like MC) performing
output onto alternate screen.
Optimize SIGWINCH Shell notification

Fixes issue with missed SIGWINCH shell notification in case the
Terminal frame was resized by using any of "Settings"->"Window size"
menu items.

Fixes #9293 - original problem was pointed out by Ziusudra. Thank you!
Remove useless font style/family settings defaults

No need for PREF_HALF_FONT_FAMILY/_STYLE defaults to be defined explicitly,
these entries will be filled with corresponding params of the current system
fixed font if they are not available from the settings file.

Fixes #9531.
Improve handling of mbyte chars in UTF8Char::IsSpace

* Switch UTF8Char's IsSpace, IsAlNum, ToLower functions to use
  system-wide BUnicodeChar service routines;
* Switch TermView::CharClassifier to use UTF8Char instead of
  raw char* string ponter. That reduces count of conversions
  and simplify code;

  Fixes #7423.