Reactions: Add more button (#1314)

* Add expand/collapse UI for reactions

- Adds a CollapsibleFlowLayout for controlling the layout
- Adds tests for  this layout and some mocks for testing layouts generally
- Improves the rendering of the reaction buttons which were not pixel perfect
- Adds the UI for the expand collapse buttons including the count of hidden items in the collapsed state.

* Add comment for reactionsCollapsed binding.

* Add the add more button and change the layout to be reactions specific and account for the add more button specifics.

* Update CollapsibleReactionLayout.swift

* Rename lines to rows, to hopefully ease the incoming merge.

* Add LayoutValueKey to organise subviews by item type.

- create ReactionLayoutItemType to tag subviews with ReactionLayoutItem
- Add LayoutValueKey support to the layout mocks
- Fix some mistakes in the merge
- Make the test code a bit more DRY
- Make the animation of the addMore and collapse buttons consistent

* Fix naming of the add more button label

* Address comments and fix padding

- Fix typos
- Use pdf/svg for icon
- Fix incorrect padding from a bad merge

* Fix "Add more" button padding to match designs

* Update snapshot test reference images.

* Fix naming, add Preserves Vector Data

ElementX/Resources/Localizations/en.lproj/Localizable.strings

@@ -449,6 +449,8 @@
 "screen_room_details_topic_title" = "Topic";
 "screen_room_error_failed_processing_media" = "Failed processing media to upload, please try again.";
 "screen_room_retry_send_menu_remove_action" = "Remove";
+"screen_room_reactions_show_more" = "Show more";
+"screen_room_reactions_show_less" = "Show less";
 "screen_session_verification_cancelled_title" = "Verification cancelled";
 "screen_session_verification_positive_button_ready" = "Start";
 "screen_signout_confirmation_dialog_submit" = "Sign out";