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/utils/utils.ts b/client/src/utils/utils.ts
index d51fa1b..794fb92 100644
--- a/client/src/utils/utils.ts
+++ b/client/src/utils/utils.ts
@@ -35,3 +35,11 @@
   sinkId?: string;
   setSinkId?: (deviceId: string) => void;
 }
+
+export type PartialNotOptional<T> = {
+  [P in keyof T]: T[P] | undefined;
+};
+
+export const isRequired = <T>(obj: Partial<T>): obj is T => {
+  return Object.values(obj).every((v) => v !== undefined);
+};