patch 9.0.2056: no digraph for quadruple prime

Problem:  no digraph for quadruple prime
Solution: add quadruple prime digraph using 4'

closes: #13380

Signed-off-by: Jonathan Wright <quaggy@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Jonathan Wright <quaggy@gmail.com>

runtime/doc/digraph.txt

@@ -1,4 +1,4 @@
-*digraph.txt*   For Vim version 9.0.  Last change: 2023 Mar 21
+*digraph.txt*   For Vim version 9.0.  Last change: 2023 Oct 20
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -174,6 +174,13 @@ ROUBLE
 The rouble sign was added in 2014 as 0x20bd.  Vim supports the digraphs =R and
 =P for this.  Note that R= and P= are other characters.
 
+QUADRUPLE PRIME
+
+The quadruple prime using the digraph 4' was added in 2023.  Although it is
+not part of RFC 1345, it supplements the existing digraph implementation as
+there already exist digraphs for PRIME, DOUBLE PRIME and TRIPLE PRIME using
+the 1', 2' and 3' digraphs.
+
 							*digraph-table*
 char  digraph	hex	dec	official name ~
 ^@	NU	0x00	  0	NULL (NUL)
@@ -931,6 +938,7 @@ char  digraph	hex	dec	official name ~
 ′	1'	2032	8242	PRIME
 ″	2'	2033	8243	DOUBLE PRIME
 ‴	3'	2034	8244	TRIPLE PRIME
+⁗	4'	2057	8279	QUADRUPLE PRIME
 ‵	1"	2035	8245	REVERSED PRIME
 ‶	2"	2036	8246	REVERSED DOUBLE PRIME
 ‷	3"	2037	8247	REVERSED TRIPLE PRIME

src/digraph.c

@@ -853,6 +853,7 @@ static digr_T digraphdefault[] = {
 	{'1', '\'', 0x2032},
 	{'2', '\'', 0x2033},
 	{'3', '\'', 0x2034},
+	{'4', '\'', 0x2057},
 	{'1', '"', 0x2035},
 	{'2', '"', 0x2036},
 	{'3', '"', 0x2037},

src/testdir/test_digraph.vim

@@ -37,6 +37,9 @@ func Test_digraphs()
   call Put_Dig("=P")
   call Put_Dig("P=")
   call assert_equal(['Р']+repeat(["₽"],2)+['П'], getline(line('.')-3,line('.')))
+  " Quadruple prime
+  call Put_Dig("'4")
+  call assert_equal("⁗", getline('.'))
   " Not a digraph
   call Put_Dig("a\<bs>")
   call Put_Dig("\<bs>a")

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2056,
 /**/
     2055,
 /**/