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>

tests/konsist/src/test/kotlin/io/element/android/tests/konsist/KonsistArchitectureTest.kt

@@ -34,6 +34,7 @@ class KonsistArchitectureTest {
             .classes()
             .withNameEndingWith("State")
             .withoutName(
+                "NoopContentValidationState",
                 "CameraPositionState",
                 "CustomSheetState",
             )

tests/konsist/src/test/kotlin/io/element/android/tests/konsist/KonsistPreviewTest.kt

@@ -145,7 +145,8 @@ class KonsistPreviewTest {
         "TextComposerVoiceNotEncryptedPreview",
         "TextComposerVoicePreview",
         "TextFieldDialogWithErrorPreview",
-        "TimelineImageWithCaptionRowPreview",
+        "TimelineItemAttachmentsViewScanningContentFailedPreview",
+        "TimelineItemAudioViewScanningContentPreview",
         "TimelineItemEventRowForDirectRoomPreview",
         "TimelineItemEventRowShieldPreview",
         "TimelineItemEventRowTimestampPreview",
@@ -155,13 +156,21 @@ class KonsistPreviewTest {
         "TimelineItemEventRowWithRRPreview",
         "TimelineItemEventRowWithReplyPreview",
         "TimelineItemEventRowWithThreadSummaryPreview",
+        "TimelineItemFileViewScanningContentPreview",
+        "TimelineItemGalleryViewScanningContentFailedPreview",
         "TimelineItemGroupedEventsRowContentCollapsePreview",
         "TimelineItemGroupedEventsRowContentExpandedPreview",
         "TimelineItemImageViewHideMediaContentPreview",
+        "TimelineItemImageViewScanningContentPreview",
         "TimelineItemRedactedMessagesGroupPreview",
+        "TimelineItemScanningContentFailedPreview",
+        "TimelineItemScanningContentWithInvalidRepliesPreview",
+        "TimelineItemScanningContentWithRepliesFailedPreview",
+        "TimelineItemStickerViewScanningContentPreview",
         "TimelineItemVideoViewHideMediaContentPreview",
+        "TimelineItemVideoViewScanningContentPreview",
+        "TimelineItemVoiceViewScanningContentPreview",
         "TimelineItemVoiceViewUnifiedPreview",
-        "TimelineVideoWithCaptionRowPreview",
         "TimelineViewMessageShieldPreview",
         "TimelineViewWithReadMarkerBothIndicatorsPreview",
         "TimelineViewWithReadMarkerJumpToUnreadIndicatorOnlyPreview",