test: move oldtests to test directory (#22536)

The new oldtest directory is in test/old/testdir. The reason for this is
that many tests have hardcoded the parent directory name to be
'testdir'.

test/old/testdir/test_autoload.vim

@@ -0,0 +1,25 @@
+" Tests for autoload
+
+set runtimepath=./sautest
+
+func Test_autoload_dict_func()
+  let g:loaded_foo_vim = 0
+  let g:called_foo_bar_echo = 0
+  call g:foo#bar.echo()
+  call assert_equal(1, g:loaded_foo_vim)
+  call assert_equal(1, g:called_foo_bar_echo)
+
+  eval 'bar'->g:foo#addFoo()->assert_equal('barfoo')
+
+  " empty name works in legacy script
+  call assert_equal('empty', foo#())
+endfunc
+
+func Test_source_autoload()
+  let g:loaded_sourced_vim = 0
+  source sautest/autoload/sourced.vim
+  call assert_equal(1, g:loaded_sourced_vim)
+endfunc
+
+
+" vim: shiftwidth=2 sts=2 expandtab