patch 8.1.2004: more functions can be used as methods

Problem:    More functions can be used as methods.
Solution:   Make various functions usable as a method.
diff --git a/src/testdir/test_swap.vim b/src/testdir/test_swap.vim
index 856c663..6e01ad0 100644
--- a/src/testdir/test_swap.vim
+++ b/src/testdir/test_swap.vim
@@ -111,7 +111,7 @@
   w
   let fname = s:swapname()
   call assert_match('Xswapinfo', fname)
-  let info = swapinfo(fname)
+  let info = fname->swapinfo()
 
   let ver = printf('VIM %d.%d', v:version / 100, v:version % 100)
   call assert_equal(ver, info.version)
@@ -153,7 +153,7 @@
   let buf = bufnr('%')
   let expected = s:swapname()
   wincmd p
-  call assert_equal(expected, swapname(buf))
+  call assert_equal(expected, buf->swapname())
 
   new Xtest3
   setlocal noswapfile