vim-patch:9.0.2056: no digraph for quadruple prime

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

closes: vim/vim#13380

47416d1a74

Co-authored-by: Jonathan Wright <quaggy@gmail.com>

runtime/doc/digraph.txt

@@ -168,6 +168,13 @@ 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* *digraph-table-mbyte*
 >
   char  digraph	hex	dec	official name
@@ -920,6 +927,7 @@ The rouble sign was added in 2014 as 0x20bd.  Vim supports the digraphs =R and
   ′	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/nvim/digraph.c

@@ -879,6 +879,7 @@ static digr_T digraphdefault[] =
   { '1', '\'', 0x2032 },
   { '2', '\'', 0x2033 },
   { '3', '\'', 0x2034 },
+  { '4', '\'', 0x2057 },
   { '1', '"', 0x2035 },
   { '2', '"', 0x2036 },
   { '3', '"', 0x2037 },

test/old/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")