Improve accessibility of the timeline (#4579)

* Make whole messages selectable and readable as a single unit when possible.
* Make most UI components not clickable when talkback is enabled.
* Make voice messages work with talkback too.
* Read grouped state events even if the events are collapsed.
* Move image and video item actions to the timeline item.
* Improve accessibility in the message context menu too
* Fix a11y issue on add attachment button.
* Add `contentDescription` to file icon so it's read aloud

---------

Co-authored-by: Benoit Marty <benoit@matrix.org>

libraries/textcomposer/impl/src/main/kotlin/io/element/android/libraries/textcomposer/TextComposer.kt

@@ -148,6 +148,7 @@ fun TextComposer(
                     IconColorButton(
                         onClick = onAddAttachment,
                         imageVector = CompoundIcons.Plus(),
+                        contentDescription = stringResource(R.string.rich_text_editor_a11y_add_attachment),
                     )
                 }
             }
@@ -292,6 +293,7 @@ fun TextComposer(
                 IconColorButton(
                     onClick = onDismissTextFormatting,
                     imageVector = CompoundIcons.Close(),
+                    contentDescription = stringResource(CommonStrings.action_close),
                 )
             },
             textFormatting = textFormattingOptions,