Content scanner (Element Pro): scan timeline events for unsafe content (#7159)

* Simplify how event content with captions are displayed

The caption component will now be added in `TimelineItemEventContentView` instead of separately in each `TimelineItem__View` component

* Make sure `CoilMediaFetcher` methods to fetch media throw errors

We need to catch them later to check if the content scanner marked some thumbnails or medias as invalid/unsafe in `AsyncImage` instances

* Add a `ContentScannerService` that allows us to manually scan a list of medias in an event and then update and store the results

The results take the form of `ContentValidationValue`, stored in a `ContentValidationState` instance tied to the event

* Create `EventContentValidationCache` to keep the `ContentValidationStates` for events in a room

* Expose `EventContentValidationCache` to Compose using `LocalEventContentValidationState`

Also add a couple of helper functions to avoid having to manually remember the states

* Use the new components to display invalid content in the timeline items

* Add `blurhash` to most media items so we can use it while validating the thumbnails/medias

* Fix custom layout issues with screenshot and UI tests

* Also check the validation state for replied-to events in the composer

* Fix and add tests

* Handle unrecoverable content validation errors too: display a 'not found' UI

* Improve the performance of `EqualWidthColumn` for the single item case

* Update screenshots

---------

Co-authored-by: ElementBot <android@element.io>

libraries/matrixmedia/impl/src/main/kotlin/io/element/android/libraries/matrix/ui/media/CoilMediaFetcher.kt

@@ -40,7 +40,7 @@ internal class CoilMediaFetcher(
                     onSuccess = { it },
                     onFailure = { error ->
                         if (error.isNetworkError()) {
-                            null
+                            throw error
                         } else {
                             fetchContent(mediaSource)
                         }
@@ -73,7 +73,7 @@ internal class CoilMediaFetcher(
             .onFailure {
                 Timber.e(it)
             }
-            .getOrNull()
+            .getOrThrow()
     }
 
     private suspend fun fetchContent(mediaSource: MediaSource): FetchResult? {
@@ -83,7 +83,7 @@ internal class CoilMediaFetcher(
             byteArray.asSourceResult()
         }.onFailure {
             Timber.e(it)
-        }.getOrNull()
+        }.getOrThrow()
     }
 
     private suspend fun fetchThumbnail(mediaSource: MediaSource, kind: MediaRequestData.Kind.Thumbnail): Result<FetchResult> {