patch 8.1.1954: more functions can be used as a method

Problem:    More functions can be used as a method.
Solution:   Allow more functions to be used as a method.
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 2ffdc24..926713e 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -883,7 +883,7 @@
   call assert_equal([-1, -1, 1, 1, 2, 2, 2, 3, 3, -1],
   \                 map(range(-1, 8), 'v:val->byte2line()'))
   call assert_equal([-1, -1, 1, 3, 6, 8, -1],
-  \                 map(range(-1, 5), 'line2byte(v:val)'))
+  \                 map(range(-1, 5), 'v:val->line2byte()'))
 
   set fileformat=dos
   call assert_equal([-1, -1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, -1],
@@ -1351,17 +1351,17 @@
   endif
 
   if has('win32')
-    call assert_equal($USERPROFILE, libcall(libc, 'getenv', 'USERPROFILE'))
+    call assert_equal($USERPROFILE, 'USERPROFILE'->libcall(libc, 'getenv'))
   else
-    call assert_equal($HOME, libcall(libc, 'getenv', 'HOME'))
+    call assert_equal($HOME, 'HOME'->libcall(libc, 'getenv'))
   endif
 
   " If function returns NULL, libcall() should return an empty string.
   call assert_equal('', libcall(libc, 'getenv', 'X_ENV_DOES_NOT_EXIT'))
 
   " Test libcallnr() with string and integer argument.
-  call assert_equal(4, libcallnr(libc, 'strlen', 'abcd'))
-  call assert_equal(char2nr('A'), libcallnr(libc, 'toupper', char2nr('a')))
+  call assert_equal(4, 'abcd'->libcallnr(libc, 'strlen'))
+  call assert_equal(char2nr('A'), char2nr('a')->libcallnr(libc, 'toupper'))
 
   call assert_fails("call libcall(libc, 'Xdoesnotexist_', '')", 'E364:')
   call assert_fails("call libcallnr(libc, 'Xdoesnotexist_', '')", 'E364:')