patch 8.1.1993: 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_searchpos.vim b/src/testdir/test_searchpos.vim
index 8dffddc..5827cbc 100644
--- a/src/testdir/test_searchpos.vim
+++ b/src/testdir/test_searchpos.vim
@@ -7,7 +7,7 @@
   call cursor(1, 1)
   call assert_equal([1, 1, 2], searchpos('\%(\([a-z]\)\|\_.\)\{-}xyz', 'pcW'))
   call cursor(1, 2)
-  call assert_equal([2, 1, 1], searchpos('\%(\([a-z]\)\|\_.\)\{-}xyz', 'pcW'))
+  call assert_equal([2, 1, 1], '\%(\([a-z]\)\|\_.\)\{-}xyz'->searchpos('pcW'))
   set cpo-=c
   call cursor(1, 2)
   call assert_equal([1, 2, 2], searchpos('\%(\([a-z]\)\|\_.\)\{-}xyz', 'pcW'))