Fix components rerendering unnecessarily

Before, some providers (WebRtcProvider, CallProvider...) were rendered conditionally.
This was causing all their children to re-render when the provider rendered.

Instead of using conditional rendering, these providers now use `ConditionalContextProvider`.
It always renders the provider, but sets its value to `initialValue` if the dependencies are not all defined.
If all dependencies are defined, the value is the result of the `useProviderValue` hook.

Changes:
- New file: `ConditionalContextProvider`
- New file: `HookComponent` - Component that calls a hook when mounted and calls a `callback` function with the hook result as argument
- For `WebRtcProvider` and `CallProvider`, use `createOptionalContext` to create the context and `ConditionalContextProvider` to provide their value only when the conditions are met
- In `WebRtcProvider`, set the webRtcConnection to undefined when not in a call
- For all providers, wrap their `value` prop in `useMemo` to avoid unnecessary rerenders

Change-Id: Ide947e216d54599aabc71cf4bd026bd20d6e0daf
diff --git a/client/src/components/CallChatDrawer.tsx b/client/src/components/CallChatDrawer.tsx
index ef5cf04..b87f37d 100644
--- a/client/src/components/CallChatDrawer.tsx
+++ b/client/src/components/CallChatDrawer.tsx
@@ -16,9 +16,8 @@
  * <https://www.gnu.org/licenses/>.
  */
 import { Divider, Stack, Typography } from '@mui/material';
-import { useContext } from 'react';
 
-import { CallContext } from '../contexts/CallProvider';
+import { useCallContext } from '../contexts/CallProvider';
 import { useConversationContext } from '../contexts/ConversationProvider';
 import ChatInterface from '../pages/ChatInterface';
 import { CloseButton } from './Button';
@@ -44,7 +43,7 @@
 };
 
 const CallChatDrawerHeader = () => {
-  const { setIsChatShown } = useContext(CallContext);
+  const { setIsChatShown } = useCallContext();
   const { conversation } = useConversationContext();
 
   // TODO: Improve this to support multiple members