Derive icon paths (#17816)

This PR improves adding and working with icons by using the new
`DerivePathStr` to derive icon paths.

This means paths no longer need to be manually specified, and the
`IconName` and file name will always be consistent between icons.

This PR does not do any work to standardize icons visually, remove
unused icons, or any other such cleanup.

Release Notes:

- N/A

crates/assistant/src/assistant_panel.rs

@@ -4110,7 +4110,7 @@ impl ContextEditor {
                         h_flex()
                             .gap_3()
                             .child(
-                                Icon::new(IconName::ExclamationTriangle)
+                                Icon::new(IconName::Warning)
                                     .size(IconSize::Small)
                                     .color(Color::Warning),
                             )
@@ -5235,7 +5235,7 @@ fn quote_selection_fold_placeholder(title: String, editor: WeakView<Editor>) ->
                 ButtonLike::new(fold_id)
                     .style(ButtonStyle::Filled)
                     .layer(ElevationIndex::ElevatedSurface)
-                    .child(Icon::new(IconName::TextSelect))
+                    .child(Icon::new(IconName::CursorIBeam))
                     .child(Label::new(title.clone()).single_line())
                     .on_click(move |_, cx| {
                         editor
@@ -5339,7 +5339,7 @@ fn render_docs_slash_command_trailer(
             div()
                 .id(("latest-error", row.0))
                 .child(
-                    Icon::new(IconName::ExclamationTriangle)
+                    Icon::new(IconName::Warning)
                         .size(IconSize::Small)
                         .color(Color::Warning),
                 )

crates/assistant/src/inline_assistant.rs

@@ -1478,7 +1478,7 @@ impl Render for PromptEditor {
                     .child(
                         ModelSelector::new(
                             self.fs.clone(),
-                            IconButton::new("context", IconName::SlidersAlt)
+                            IconButton::new("context", IconName::SettingsAlt)
                                 .shape(IconButtonShape::Square)
                                 .icon_size(IconSize::Small)
                                 .icon_color(Color::Muted)

crates/assistant/src/slash_command/diagnostics_command.rs

@@ -193,11 +193,11 @@ impl SlashCommand for DiagnosticsSlashCommand {
                 .map(|(range, placeholder_type)| SlashCommandOutputSection {
                     range,
                     icon: match placeholder_type {
-                        PlaceholderType::Root(_, _) => IconName::ExclamationTriangle,
+                        PlaceholderType::Root(_, _) => IconName::Warning,
                         PlaceholderType::File(_) => IconName::File,
                         PlaceholderType::Diagnostic(DiagnosticType::Error, _) => IconName::XCircle,
                         PlaceholderType::Diagnostic(DiagnosticType::Warning, _) => {
-                            IconName::ExclamationTriangle
+                            IconName::Warning
                         }
                     },
                     label: match placeholder_type {

crates/assistant/src/terminal_inline_assistant.rs

@@ -585,7 +585,7 @@ impl Render for PromptEditor {
                     .gap_2()
                     .child(ModelSelector::new(
                         self.fs.clone(),
-                        IconButton::new("context", IconName::SlidersAlt)
+                        IconButton::new("context", IconName::SettingsAlt)
                             .shape(IconButtonShape::Square)
                             .icon_size(IconSize::Small)
                             .icon_color(Color::Muted)