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_spell.vim b/src/testdir/test_spell.vim
index af72637..a44d955 100644
--- a/src/testdir/test_spell.vim
+++ b/src/testdir/test_spell.vim
@@ -73,7 +73,7 @@
   set spell
 
   call assert_equal(['bycycle', 'bad'],  spellbadword('My bycycle.'))
-  call assert_equal(['another', 'caps'], spellbadword('A sentence. another sentence'))
+  call assert_equal(['another', 'caps'], 'A sentence. another sentence'->spellbadword())
 
   set spelllang=en
   call assert_equal(['', ''],            spellbadword('centre'))
@@ -179,7 +179,7 @@
         \ )
 
   call assert_equal("gebletegek", soundfold('goobledygoook'))
-  call assert_equal("kepereneven", soundfold('kóopërÿnôven'))
+  call assert_equal("kepereneven", 'kóopërÿnôven'->soundfold())
   call assert_equal("everles gesvets etele", soundfold('oeverloos gezwets edale'))
 endfunc
 
@@ -440,7 +440,7 @@
       break
     endif
     let prevbad = bad
-    let lst = spellsuggest(bad, 3)
+    let lst = bad->spellsuggest(3)
     normal mm
 
     call add(result, [bad, lst])