Modernize how we use React contexts (#3359)

* Replace useContext with use

The docs recommend the use hook because it is simpler and allows itself to be called conditionally.

* Simplify our context providers

React 19 lets you omit the '.Provider' bit.

src/room/GroupCallView.test.tsx

@@ -149,7 +149,7 @@ function createGroupCallView(
   const { getByText } = render(
     <BrowserRouter>
       <TooltipProvider>
-        <MediaDevicesContext.Provider value={mockMediaDevices({})}>
+        <MediaDevicesContext value={mockMediaDevices({})}>
           <ProcessorProvider>
             <GroupCallView
               client={client}
@@ -164,7 +164,7 @@ function createGroupCallView(
               widget={widget}
             />
           </ProcessorProvider>
-        </MediaDevicesContext.Provider>
+        </MediaDevicesContext>
       </TooltipProvider>
     </BrowserRouter>,
   );