Sync top/bottom bar disappearance to the scroll (#1855)

* Disable existing code that toggles shell

* Make shell mode a float

* Translate based on the gesture

* Track header and footer heights

* Add web support

* Fix types and cleanup

* Add back isScrolled logic

* Add comments

src/state/shell/shell-layout.tsx

@@ -0,0 +1,41 @@
+import React from 'react'
+import {SharedValue, useSharedValue} from 'react-native-reanimated'
+
+type StateContext = {
+  headerHeight: SharedValue<number>
+  footerHeight: SharedValue<number>
+}
+
+const stateContext = React.createContext<StateContext>({
+  headerHeight: {
+    value: 0,
+    addListener() {},
+    removeListener() {},
+    modify() {},
+  },
+  footerHeight: {
+    value: 0,
+    addListener() {},
+    removeListener() {},
+    modify() {},
+  },
+})
+
+export function Provider({children}: React.PropsWithChildren<{}>) {
+  const headerHeight = useSharedValue(0)
+  const footerHeight = useSharedValue(0)
+
+  const value = React.useMemo(
+    () => ({
+      headerHeight,
+      footerHeight,
+    }),
+    [headerHeight, footerHeight],
+  )
+
+  return <stateContext.Provider value={value}>{children}</stateContext.Provider>
+}
+
+export function useShellLayout() {
+  return React.useContext(stateContext)
+}