Files · Items: one icon map, file icon, file row and file grid

The crate had two maps from a file's name to its icon, in chat and in the
file tree, and they disagreed. One map now lives in primitives, over the
Lucide file-* icons, and chat, agent, the file tree and the directory
listing use it. FileIcon draws it for a file or a folder. FileItem is a
file's row, a ListItem with its size and when it changed. FileList is the
directory listing. FileGrid lays tiles in the order given, with a cursor
seeded from the owner's pick: arrows by tile and by row, Home, End, Enter
and a double press to open. The count of what fits a width has one home,
layout's columns_for, and fit builds on it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/files/icon.rs

@@ -0,0 +1,55 @@
+use gpui::{App, IntoElement, RenderOnce, Window};
+
+use crate::{
+    lists::DirEntry,
+    primitives::{Icon, IconName, file_icon},
+    theme::{ActiveTheme, IconSize},
+};
+
+/// A file's icon by its name's extension, or a folder's, open or shut.
+#[derive(IntoElement)]
+pub struct FileIcon {
+    icon: IconName,
+    size: IconSize,
+}
+
+impl FileIcon {
+    pub fn file(name: impl AsRef<str>) -> Self {
+        Self {
+            icon: file_icon(name.as_ref()),
+            size: IconSize::Md,
+        }
+    }
+
+    pub fn folder(open: bool) -> Self {
+        Self {
+            icon: if open {
+                IconName::FolderOpen
+            } else {
+                IconName::Folder
+            },
+            size: IconSize::Md,
+        }
+    }
+
+    /// The icon for a listing's entry: a shut folder, or the file's by its name.
+    pub fn entry(entry: &DirEntry) -> Self {
+        match entry.is_folder() {
+            true => Self::folder(false),
+            false => Self::file(entry.name()),
+        }
+    }
+
+    pub fn size(mut self, size: IconSize) -> Self {
+        self.size = size;
+        self
+    }
+}
+
+impl RenderOnce for FileIcon {
+    fn render(self, _: &mut Window, cx: &mut App) -> impl IntoElement {
+        Icon::new(self.icon)
+            .size(self.size)
+            .color(cx.theme().colors.fg_muted)
+    }
+}