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/git_ui/src/git_ui.rs

@@ -356,7 +356,7 @@ mod remote_button {
             "Publish",
             0,
             0,
-            Some(IconName::ArrowUpFromLine),
+            Some(IconName::ExpandUp),
             keybinding_target.clone(),
             move |_, window, cx| {
                 window.dispatch_action(Box::new(git::Push), cx);
@@ -383,7 +383,7 @@ mod remote_button {
             "Republish",
             0,
             0,
-            Some(IconName::ArrowUpFromLine),
+            Some(IconName::ExpandUp),
             keybinding_target.clone(),
             move |_, window, cx| {
                 window.dispatch_action(Box::new(git::Push), cx);
@@ -438,7 +438,7 @@ mod remote_button {
                     .child(
                         div()
                             .px_1()
-                            .child(Icon::new(IconName::ChevronDownSmall).size(IconSize::XSmall)),
+                            .child(Icon::new(IconName::ChevronDown).size(IconSize::XSmall)),
                     ),
             )
             .menu(move |window, cx| {