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

layouts/docs/baseof.html

@@ -13,16 +13,18 @@
 		{{ end }}
     {{ block "announcement" . }}{{ partial "announcement.html" . }}{{ end }}
 		{{ block "deprecation" . }}{{ partial "deprecation-warning.html" . }}{{ end }}
-		<section id="encyclopedia">
-			{{ block "side-menu" . }}<div id="docsToc" style="display:none;"></div>{{ end }}
-			<div id="{{ block "content-id" . }}docsContent{{ end }}">
-        {{ block "content" . }}{{ end }}
-
-        {{ partial "feedback.html" . }}
-
-        {{ partial "git-info.html" . }}
-			</div>
-		</section>
+    <main>
+        <section id="encyclopedia">
+          {{ block "side-menu" . }}<div id="docsToc" style="display:none;"></div>{{ end }}
+          <div id="{{ block "content-id" . }}docsContent{{ end }}">
+            {{ block "content" . }}{{ end }}
+    
+            {{ partial "feedback.html" . }}
+    
+            {{ partial "git-info.html" . }}
+          </div>
+        </section>
+    </main>
 		{{ partialCached "footer.html" . }}
 		{{ partialCached "footer-scripts.html" . }}
     <script language="application/javascript">