runtime(vim): Update base-syntax, fix nested function folding (#14397)

Only match function folding start and end patterns at the start of a
line, excluding heredocs and :append/:change/:insert commands.

Fixes #14393

Signed-off-by: Christian Brabandt <cb@256bit.org>
Signed-off-by: Doug Kearns <dougkearns@gmail.com>

runtime/syntax/testdir/input/vim_ex_function_fold.vim

@@ -181,3 +181,43 @@ delfunction foo.bar
 delfunction! Foo
 delfunction foo.bar
 
+
+" fold-region ending
+
+function Foo()
+  " endfunction
+endfunction
+
+function Foo()
+  echo "endfunction"
+endfunction
+
+function Foo()
+  let x =<< END
+    endfunction
+  END
+
+endfunction
+
+function Foo()
+  append
+    endfunction
+.
+endfunction
+
+function Foo()
+  change
+    endfunction
+.
+
+endfunction
+
+function Foo()
+  insert
+    endfunction
+.
+endfunction
+
+:function Foo()
+:endfunction
+