Expose the push notification settings

[giomfo]

The RustSDK defines the push rules in the ruma-common crate, but does not currently expose them.

In order to allow the user to view and update the notification settings, we need to expose these rules in the ffi layer of the SDK.

We have two options:

• Expose the Ruleset (the internal type that contains the push rules) directly, but this means exposing also all the internal types and associated methods used by the SDK to store, get, create and delete a push rule.
• Expose only a set of methods and enumerations to get and update push rules.

The second option seems to be the best, as it will allow the management of notification settings to be shared between iOS and Android.

A minimal set of features to expose should be:

• Room notification settings ([Story] Notification settings for a room element-hq/element-meta#1075):

  • an enumeration defining the different notification modes: AllMessages, MentionsAndKeywordsOnly, Mute
  • a method to check if a given room has a user-defined notification mode or if it uses the default one.
  • a method to get the current notification mode
  • some methods to define the notification mode
    • set a custom mode
    • remove a custom mode (switch back to the default)

• Global notification settings ([Story] Add application settings screen for notifications element-hq/element-meta#1676):

  • an enumeration defining the predefined push rules (.m.rule.master, .m.rule.room_one_to_one, …) to check/enable/disable them
  • [optional] a method to manage the keyword push rules (one global content rule per keyword)
  • consider the intentional mentions rules (see MSC3952: Intentional Mentions)
  • a method to list all rooms with a user defined rule activated

Also, the SDK should be able to notify the application when push rules are updated after a sync response.

• Update the application on push rules changes

Out of scope

• a method to manage the keyword push rules (one global content rule per keyword)

[giomfo]

About notification settings handling. We made the following decisions:
1- user mentions are considered enabled at the SDK level as soon as one of the 3 push rules is enabled
2- room mentions are considered enabled at the SDK level as soon as one of the 2 push rules is enabled
3 (edited)- at the account level (Global settings), if all mentions and potential keyword rules are disabled, we will display a banner to let the user know we are not able to handle the Notification Settings in EX. If the user wants to unblock this situation, he may click on a button -> we force user mentions ON (the 3 push rules)
4 (edited)- at the room level, if a push rule has been created in global/room section with ruleId = roomId and action = "don't notify", we consider a custom setting: "Mentions & Keywords". If all mentions and potential keyword rules are disabled, we display a warning in EX room Notifications screen.
5 (edited)- if all mentions and potential keyword rules are disabled, we display a warning in the EX room Notifications screen when the user turns on the custom toggle.

[giomfo]

I consider this task "Done"