test: Product Query & Filter Engine, Item Group Page

- Test for ProductQuery engine and ProductFilters engine
- Test for engine for Item Group too
- Renamed ‘product_configurator’ to ‘variant_selector’
- Cleaned up filters.py
- Modal freeze backdrop lighter only in cart, since there’s nothing over it
- Fixed unusual spacing in variant selector dialog
- Made `get_child_groups_for_website` more readable
- Replaced ‘Configure’ with ‘Select’ for variant selection

erpnext/public/scss/shopping_cart.scss

@@ -502,12 +502,7 @@ body.product-page {
 }
 
 .item-configurator-dialog {
-	.modal-header {
-		padding: var(--padding-md) var(--padding-xl);
-	}
-
 	.modal-body {
-		padding: 0 var(--padding-xl);
 		padding-bottom: var(--padding-xl);
 
 		.status-area {
@@ -1292,13 +1287,10 @@ body.product-page {
 	font-size: 72px;
 }
 
-.modal-backdrop {
-	position: fixed;
-	top: 0;
-	right: 0;
-	left: 0;
-	background-color: var(--gray-100);
-	height: 100%;
+[data-path="cart"] {
+	.modal-backdrop {
+		background-color: var(--gray-50); // lighter backdrop only on cart freeze
+	}
 }
 
 .item-thumb {