Add bridge page controller and helpers.

app/javascript/bridge/helpers/viewport.js

@@ -0,0 +1,19 @@
+let top = 0
+
+export const viewport = {
+  get top() {
+    return top
+  },
+  get height() {
+    return visualViewport.height
+  }
+}
+
+function update() {
+  requestAnimationFrame(() => {
+    top = parseInt(getComputedStyle(document.documentElement).getPropertyValue("--safe-area-inset-top"))
+  })
+}
+
+visualViewport.addEventListener("resize", update)
+update()