feat(eval/method): partially port v8.1.1993

Problem:    More functions can be used as methods.
Solution:   Make various functions usable as a method.
196b466443

server2client requires +clientserver, which hasn't been ported yet.
The eval.txt docs and test_clientserver.vim tests for server2client already exist, so include those
changes.

test_bufline.vim: Test for setbufline requires v8.1.1189 (which was reverted in #10848).

src/nvim/testdir/test_environ.vim

@@ -22,7 +22,7 @@ endfunc
 
 func Test_setenv()
   unlet! $TESTENV
-  call setenv('TEST ENV', 'foo')
+  eval 'foo'->setenv('TEST ENV')
   call assert_equal('foo', getenv('TEST ENV'))
   call setenv('TEST ENV', v:null)
   call assert_equal(v:null, getenv('TEST ENV'))