Redesign and clean up all icons across Zed (#35856)

- [x] Clean up unused and old icons
- [x] Swap SVG for all in-use icons with the redesigned version
- [x] Document guidelines

Release Notes:

- N/A

crates/debugger_ui/src/session/running/breakpoint_list.rs

@@ -681,7 +681,7 @@ impl BreakpointList {
                 }),
             )
             .child(
-                IconButton::new("remove-breakpoint-breakpoint-list", IconName::X)
+                IconButton::new("remove-breakpoint-breakpoint-list", IconName::Close)
                     .icon_size(IconSize::XSmall)
                     .icon_color(ui::Color::Error)
                     .when_some(remove_breakpoint_tooltip, |this, tooltip| {
@@ -1439,7 +1439,7 @@ impl RenderOnce for BreakpointOptionsStrip {
                     .child(
                         IconButton::new(
                             SharedString::from(format!("{id}-log-toggle")),
-                            IconName::ScrollText,
+                            IconName::Notepad,
                         )
                         .icon_size(IconSize::XSmall)
                         .style(style_for_toggle(ActiveBreakpointStripMode::Log, has_logs))

crates/debugger_ui/src/session/running/console.rs

@@ -352,7 +352,7 @@ impl Console {
                     .child(
                         div()
                             .px_1()
-                            .child(Icon::new(IconName::ChevronDownSmall).size(IconSize::XSmall)),
+                            .child(Icon::new(IconName::ChevronDown).size(IconSize::XSmall)),
                     ),
             )
             .when(

crates/debugger_ui/src/session/running/stack_frame_list.rs

@@ -493,7 +493,7 @@ impl StackFrameList {
                             .child(
                                 IconButton::new(
                                     ("restart-stack-frame", stack_frame.id),
-                                    IconName::DebugRestart,
+                                    IconName::RotateCcw,
                                 )
                                 .icon_size(IconSize::Small)
                                 .on_click(cx.listener({