Rename IconElement to just Icon (#3974)

This PR renames the `IconElement` component to just `Icon`.

This better matches the rest of our components, as `IconElement` was the
only one using this naming convention.

The `Icon` enum has been renamed to `IconName` to free up the name.

I was trying to come up with a way that would allow rendering an
`Icon::Zed` directly (and thus make the `IconElement` a hidden part of
the API), but I couldn't come up with a way to do this cleanly.

Release Notes:

- N/A

crates/terminal_view/src/terminal_view.rs

@@ -20,7 +20,7 @@ use terminal::{
     Clear, Copy, Event, MaybeNavigationTarget, Paste, ShowCharacterPalette, Terminal,
 };
 use terminal_element::TerminalElement;
-use ui::{h_stack, prelude::*, ContextMenu, Icon, IconElement, Label};
+use ui::{h_stack, prelude::*, ContextMenu, Icon, IconName, Label};
 use util::{paths::PathLikeWithPosition, ResultExt};
 use workspace::{
     item::{BreadcrumbText, Item, ItemEvent},
@@ -690,7 +690,7 @@ impl Item for TerminalView {
         let title = self.terminal().read(cx).title(true);
         h_stack()
             .gap_2()
-            .child(IconElement::new(Icon::Terminal))
+            .child(Icon::new(IconName::Terminal))
             .child(Label::new(title).color(if selected {
                 Color::Default
             } else {