vim-patch:9.1.0101: upper-case of German sharp s should be U+1E9E (#27449)

Problem:  upper-case of ß should be U+1E9E (CAPITAL LETTER SHARP S)
          (fenuks)
Solution: Make gU, ~ and g~ convert the U+00DF LATIN SMALL LETTER SHARP S (ß)
          to U+1E9E LATIN CAPITAL LETTER SHARP S (ẞ), update tests
          (glepnir)

This is part of Unicode 5.1.0 from April 2008, so should be fairly safe
to use now and since 2017 is part of the German standard orthography,
according to Wikipedia:
https://en.wikipedia.org/wiki/Capital_%E1%BA%9E#cite_note-auto-12

There is however one exception: UnicodeData.txt for U+00DF
LATIN SMALL LETTER SHARP S does NOT define U+1E9E LATIN CAPITAL LETTER
SHARP S as its upper case version. Therefore, toupper() won't be able
to convert from lower sharp s to upper case sharp s (the other way
around however works, since U+00DF is considered the lower case
character of U+1E9E and therefore tolower() works correctly for the
upper case version).

fixes: vim/vim#5573
closes: vim/vim#14018

bd1232a1fa

Co-authored-by: glepnir <glephunter@gmail.com>

test/functional/legacy/039_visual_block_mode_commands_spec.lua

@@ -134,7 +134,7 @@ describe('Visual block mode', function()
   end)
 
   it('should make a selected part uppercase', function()
-    -- GUe must uppercase a whole word, also when ß changes to SS.
+    -- GUe must uppercase a whole word, also when ß changes to ẞ.
     feed('Gothe youtußeuu end<ESC>Ypk0wgUe<CR>')
     -- GUfx must uppercase until x, inclusive.
     feed('O- youßtußexu -<ESC>0fogUfx<CR>')
@@ -150,13 +150,13 @@ describe('Visual block mode', function()
 
     expect([[
       
-      the YOUTUSSEUU end
-      - yOUSSTUSSEXu -
-      THE YOUTUSSEUU END
-      111THE YOUTUSSEUU END
+      the YOUTUẞEUU end
+      - yOUẞTUẞEXu -
+      THE YOUTUẞEUU END
+      111THE YOUTUẞEUU END
       BLAH DI
       DOH DUT
-      222the yoUTUSSEUU END
+      222the yoUTUẞEUU END
       333THE YOUTUßeuu end]])
   end)