patch 9.1.1640: Unicode has deprecated some code-points

Problem:  Unicode has deprecated some code-points
Solution: Update the digraph tables to align with the Unicode v16
          release (David Friant)

This commit updates the digraphs Left-Pointing Angle Bracket '</'
and Right-Pointing Angle Bracket '/>' to account for the fact that
the old Unicode codepoints for them (2329 and 232A, respectively)
have been deprecated. As per the Miscellaneous Technical code chart
(https://www.unicode.org/charts/PDF/U2300.pdf), the old digraphs
have been reassigned to the CJK Left Angle Bracket and Right Angle
Bracket (3008 and 3009) with their declaration moved to the
appropriate block.

This commit also introduces the new digraphs '<[' and ']>' to
represent the Mathematical Left Angle Bracket and Mathematical
Right Angle Bracket (27E8 and 27E9) to replace the deprecated code
points in the Technical block.

Tests have been added and, I believe, the documentation has been
updated accordingly.

closes: #17990

Signed-off-by: David Friant <friant@HPEnvyx360.friant.dev>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/version9.txt

@@ -1,4 +1,4 @@
-*version9.txt*  For Vim version 9.1.  Last change: 2025 Aug 12
+*version9.txt*  For Vim version 9.1.  Last change: 2025 Aug 16
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -41739,6 +41739,12 @@ Others: ~
 - The close button shown in the non-GUI 'tabline' will only be visible if the
   'mouse' option contains either "a" or any of the flags "n", "v", or "i".
 - |C-indenting| handles compound literals.
+- The digraphs "</" (LEFT-POINTING ANGLE BRACKET) and ">/" (RIGHT-POINTING
+  ANGLE BRACKET) have been changed to represent LEFT ANGLE BRACKET and RIGHT
+  ANGLE BRACKET to match the Unicode Miscellaneous Technical code chart from
+  Unicode 16.
+- Two additional digraphs have been added: LEFT ANGLE BRACKET "<[" and RIGHT
+  ANGLE BRACKET "]>".
 
 							*added-9.2*
 Added ~