[SDK-3627] Make buildLogoutUrl internal only and replace with onRedirect handler on logout

[ewanharris]

Changes

Similar to #948/#980 this removes buildLogoutUrl from the public API making it an internal private API, and instead adds a similar onRedirect handler that will perform the redirection, continuing to use window.location.assign if not provided. This change has the consequence that the logout method is no longer synchronous and must always be await-ed

For those that used buildLogoutUrl the change looks as follows

- const url = client.buildLogoutUrl();
- await Browser.open({ url })
+ await client.logout({
+   onRedirect: async (url) => {
+     await Browser.open({ url });
+   }
+ });

If you were previously using localOnly, this should be replaced with a handler that does nothing, like so:

- client.logout({
-   localOnly: true
- });
+ await client.logout({
+    onRedirect: async (url) => { }
+ });

Internally, this also removes the clearSync function on CacheManager as given that the logout now always returns a Promise we no longer need to switch to a synchronous method to remove the keys and prevent race conditions

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All code quality tools/guidelines have been run/followed