patch 8.1.0286: 'incsearch' does not apply to :smagic and :snomagic

Problem:    'incsearch' does not apply to :smagic and :snomagic.
Solution:   Add support. (Hirohito Higashi)
diff --git a/src/testdir/test_search.vim b/src/testdir/test_search.vim
index a36b4fb..90a0a0e 100644
--- a/src/testdir/test_search.vim
+++ b/src/testdir/test_search.vim
@@ -384,6 +384,14 @@
   undo
   call feedkeys(":%substitute/the\<c-l>/xxx\<cr>", 'tx')
   call assert_equal('  2 xxxe', getline('.'))
+  undo
+  call feedkeys(":%smagic/the.e/xxx\<cr>", 'tx')
+  call assert_equal('  2 xxx', getline('.'))
+  undo
+  call assert_fails(":%snomagic/the.e/xxx\<cr>", 'E486')
+  "
+  call feedkeys(":%snomagic/the\\.e/xxx\<cr>", 'tx')
+  call assert_equal('  2 xxx', getline('.'))
 
   call Incsearch_cleanup()
 endfunc