T23c: AI chat, input

- PromptInput: attachments and context above the field, the owner's tools and
  send below; Enter sends, Shift-Enter breaks the line; / offers commands and
  @ offers context over forms::Suggestions; files dropped on it attach behind a
  drop veil
- AttachmentButton, AttachmentChip with thumbnails and uploads, ContextChips
- VoiceInputButton and VoiceWaveform with a red dot and the time
- ParameterPanel, SystemPromptEditor, TokenCounter, CostEstimator
- forms: a Newline action on Shift-Enter keeps one-line fields to one line;
  replace_trigger moves beside Suggestions; choose and dropped shared
- gallery: composer, pickers and tuning

src/documents/blocks/view.rs

@@ -8,7 +8,8 @@ use gpui::{
 use super::{Block, BlockData, BlockEditor, BlockKind, matching};
 use crate::{
     buttons::{ButtonVariant, IconButton},
-    documents::suggest::{Offer, offers, replace_trigger},
+    documents::suggest::{Offer, offers},
+    forms::replace_trigger,
     forms::{Backspace, Choice, Down, Enter, Pick, Redo, Submit, Undo, Up},
     menus::{Menu, MenuItem, OverflowMenu},
     motion::Reorder,