Revise and clean up some icons (#35582)

This is really just a small beginning, as there are many other icons to
be revised and cleaned up. Our current set is a bit of a mess in terms
of dimension, spacing, stroke width, and terminology. I'm sure there are
more non-used icons I'm not covering here, too. We'll hopefully tackle
it all soon leading up to 1.0.

Closes https://github.com/zed-industries/zed/issues/35576

Release Notes:

- N/A

crates/collab_ui/src/chat_panel.rs

@@ -1162,7 +1162,7 @@ impl Panel for ChatPanel {
     }
 
     fn icon(&self, _window: &Window, cx: &App) -> Option<ui::IconName> {
-        self.enabled(cx).then(|| ui::IconName::MessageBubbles)
+        self.enabled(cx).then(|| ui::IconName::Chat)
     }
 
     fn icon_tooltip(&self, _: &Window, _: &App) -> Option<&'static str> {