T22: Collaboration

- presence: avatars ringed in each peer's color with where they are, press to
  follow; a breathing live dot; follow mode frames the view and stops on Escape
- remote cursors and selections painted over a field from its own layout
- comment threads with replies, reactions and resolve; a marker that opens a
  thread in a bubble; a sidebar of open and resolved threads
- annotations washed in their authors' colors, notes on hover
- suggestion mode: edits become suggestions word by word; track changes shows
  them struck and underlined, to accept or reject
- sharing: invite by email with checked chips, roles, the access list and who
  the link lets in, in one dialog
- primitives::hold_focus gives a mode its own focus, shared with ZenMode
- AvatarGroup's tuck and count shared; Avatar::ring_color; TagInput::check;
  TextInput::bounds_for_range; Popover::size
- icons: smile-plus, user-plus, message-square-diff
- gallery: the Collaboration page with scripted states

src/forms/mod.rs

@@ -79,7 +79,9 @@ pub(crate) use mention::{Suggestions, active_trigger, handles_matching};
 pub use multi::MultiSelect;
 pub use number::{NumberInput, ScrubInput};
 pub use options::Choice;
-pub(crate) use options::{OnFlag, OnValue, Pick, Run, float, float_height, step, surface};
+pub(crate) use options::{
+    OnFlag, OnValue, OnValues, Pick, Run, float, float_height, step, surface,
+};
 pub use pairs::{FieldArray, KeyValueInput, ListInput};
 pub use path::PathInput;
 pub use pattern::{RegexInput, regex_highlights};