Implement the save action when previewing media. (#3630)

* Implement the save action on the media preview.

* Update Compound and use the correct icon.

Also fixes an icon that has been renamed.

* Update the add to photo library usage description to match the designs.

* PR comments.

project.yml

@@ -65,7 +65,7 @@ packages:
     # path: ../matrix-rust-sdk
   Compound:
     url: https://github.com/element-hq/compound-ios
-    revision: 1a70bc7f3420647843b9c18748982c61ef7d2245
+    revision: 9325643cb4d22150881c5bf79e1e6e3c5a87ea89
     # path: ../compound-ios
   AnalyticsEvents:
     url: https://github.com/matrix-org/matrix-analytics-events