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/ui.c b/src/ui.c
index 151857f..393bf91 100644
--- a/src/ui.c
+++ b/src/ui.c
@@ -1500,7 +1500,7 @@
 	    row2--;
 	}
 
-	// Handle the rectangle thats left
+	// Handle the rectangle that's left
 	if (row2 >= row1)
 	    clip_invert_rectangle(cbd, row1, 0, row2 - row1 + 1,
 							 (int)Columns, invert);