runtime(vim): Update base-syntax, highlight literal string quote escape

Match the '' escape sequence in literal strings.  These were previously
ending the current string and starting another concatenated literal
string.

closes: #16415

Signed-off-by: Christian Brabandt <cb@256bit.org>
Signed-off-by: Doug Kearns <dougkearns@gmail.com>
diff --git a/runtime/syntax/testdir/input/vim_expr.vim b/runtime/syntax/testdir/input/vim_expr.vim
index 8d30656..316f462 100644
--- a/runtime/syntax/testdir/input/vim_expr.vim
+++ b/runtime/syntax/testdir/input/vim_expr.vim
@@ -21,6 +21,15 @@
 echo "\<C->>>"
 echo "\<*C->>>"
 
+echo ''''
+echo '''foo'
+echo 'foo'''
+echo 'foo''bar'
+
+" Unreported issue (incorrectly matches as vimString vimMark vimOper NONE)
+" https://github.com/tpope/vim-unimpaired/blob/6d44a6dc2ec34607c41ec78acf81657248580bf1/plugin/unimpaired.vim#L232
+let cmd = 'put!=repeat(nr2char(10), v:count1)|silent '']+'
+
 " String interpolation
 
 echo 'Don''t highlight interpolation: {{ {1 + 2} }}'
@@ -30,6 +39,11 @@
 echo $"Highlight interpolation:\t{{ { string({"foo": "bar"}) } }}"
 echo $"Highlight interpolation:\t{{ { $"nested: {{ {1 + 2} }}" } }}"
 
+echo $''''
+echo $'''foo'
+echo $'foo'''
+echo $'foo''bar'
+
 " Number
 
 " Hexadecimal