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_stat.vim b/src/testdir/test_stat.vim
index c8830d1..ccd5950 100644
--- a/src/testdir/test_stat.vim
+++ b/src/testdir/test_stat.vim
@@ -5,7 +5,7 @@
   let times = []
   let result = 0
 
-  " Use three files istead of localtim(), with a network filesystem the file
+  " Use three files instead of localtim(), with a network filesystem the file
   " times may differ at bit
   let fl = ['Hello World!']
   for fname in fnames