[IMP] theme_test_custo: rename Img component to BuilderImg

The `Img` component has a confusing name, because in templates it looks too similar to the
HTML tag `<img>`. To improve clarity, this commit changes the name to `Image`.

task-5345698

Author: AlessandroLupo

theme_test_custo/static/src/builder/footer.xml

@@ -7,7 +7,7 @@
         <BuilderSelectItem title.translate="Custom Theme"
                 actionParam="{ view: 'theme_test_custo.template_footer_custom', vars: { 'footer-template': 'custom-theme' } }"
         >
-            <Img src="'/theme_test_custo/static/src/img/template_footer_opt.svg'" class="'theme_test_custo_footer'"/>
+            <Image src="'/theme_test_custo/static/src/img/template_footer_opt.svg'" class="'theme_test_custo_footer'"/>
         </BuilderSelectItem>
     </xpath>
 </t>

theme_test_custo/static/src/builder/header.xml

@@ -16,7 +16,7 @@
                     },
                 ]"
         >
-            <Img src="'/theme_test_custo/static/src/img/template_header_opt.svg'" class="'theme_test_custo_header'"/>
+            <Image src="'/theme_test_custo/static/src/img/template_header_opt.svg'" class="'theme_test_custo_header'"/>
         </BuilderSelectItem>
     </xpath>
 </t>