Accessibility updates - main landmark roles (#17106)

* Removed multiple main tags from home page

Signed-off-by: chaitanyakaranam <chaitanya.karanam@yahoo.com>

* Removed multiple occurances of main in case-studies page

Signed-off-by: chaitanyakaranam <chaitanya.karanam@yahoo.com>

* Replaced css for main tag with .main-section class

Signed-off-by: ChaitanyaKaranam <karanam.krishna.25@gmail.com>

* Added main landmark role for all the pages

Signed-off-by: ChaitanyaKaranam <karanam.krishna.25@gmail.com>

* Force checks.

request-checks: true

assets/sass/_tablet.sass

@@ -116,7 +116,7 @@ $feature-box-div-width: 45%
       text-align: left
       margin-bottom: 18px
 
-    main
+    main, .main-section
       position: relative
       clear: both
       display: table