Add support for posting freeform reactions on iOS

#### What would you like to do?
I would like to be able to send freeform reactions on iOS

#### Why would you like to do it?
- [MSC2677](https://github.com/uhoreg/matrix-doc/blob/aggregations-reactions/proposals/2677-reactions.md) supports reactions with long keys, i.e. text reactions
- This feature is already available through other apps and [our users can see those reactions](https://github.com/vector-im/element-android/issues/307)
- It is already possible to send freeform reactions through bots from Element, so at the moment the feature exists but is obscure
- Element users can already "+1" a freeform reaction on any platform by clicking it

#### How would you like to achieve it?
- By being able to compose a freeform reaction on iOS
- Being able to view long reactions in a user friendly way (I can't see any upper limit set by the MSC)
- Be able to [report reactions to moderators](https://github.com/matrix-org/matrix-react-sdk/pull/6628#issuecomment-1123509348)
- Remove reactions as a moderator/admin user in a room
- Seealso [this comment from Jim on moderation](https://github.com/matrix-org/matrix-react-sdk/pull/6628#issuecomment-1123509348)