patch 8.2.0156: various typos in source files and tests

Problem:    Various typos in source files and tests.
Solution:   Fix the typos. (Emir Sari, closes #5532)
diff --git a/src/testdir/test_quickfix.vim b/src/testdir/test_quickfix.vim
index b7b4281..129b1cf 100644
--- a/src/testdir/test_quickfix.vim
+++ b/src/testdir/test_quickfix.vim
@@ -2629,7 +2629,7 @@
   call assert_equal('quickfix', getwinvar(1, '&buftype'))
   call assert_equal('quickfix', getwinvar(3, '&buftype'))
 
-  " Jumping to a file from the location list window should find a usuable
+  " Jumping to a file from the location list window should find a usable
   " window by wrapping around the window list.
   enew | only
   call setloclist(0, [], 'f')