Add support for parsing and applying viewport <meta> (#35901)

This patch comprises following steps:
1. Parses the `viewport` Attribute from `<meta>`.
2. Creates a `ViewportDescription` struct.
3. Populate values into Viewport struct.
4. Pass & Stash Viewport Description to Webview.
5. Process parsed values of `viewport <meta>`

Testing: Tested locally.
Fixes: #36159

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Signed-off-by: Shubham Gupta <shubham13297@gmail.com>
Signed-off-by: Xiaocheng Hu <xiaochengh.work@gmail.com>
Co-authored-by: Xiaocheng Hu <xiaochengh.work@gmail.com>

components/compositing/tracing.rs

@@ -59,6 +59,7 @@ mod from_constellation {
                 Self::GetScreenSize(..) => target!("GetScreenSize"),
                 Self::GetAvailableScreenSize(..) => target!("GetAvailableScreenSize"),
                 Self::CollectMemoryReport(..) => target!("CollectMemoryReport"),
+                Self::Viewport(..) => target!("Viewport"),
             }
         }
     }