add ui::Vector and separate images from icons (#17815)

This PR pulls non-icon assets out of `ui::components::icon` in
preparation for icon standardization.

In the future icons will have standard names and sizes, and these image
assets won't conform to those constraints.

We can also add a `ui::components::image::Image` wrapper around the
`gpui::img` element in the future for any Zed-specific image styling we
want to enforce.

Of note:

```rust
#[derive(Debug, PartialEq, Eq, Copy, Clone, EnumIter, EnumString, IntoStaticStr, Serialize, Deserialize, DerivePathStr)]
#[strum(serialize_all = "snake_case")]
#[path_str(prefix = "images", suffix = ".svg")]
pub enum VectorName {
    ZedLogo,
    ZedXCopilot,
}
```

You can see in the above code we no longer need to manually specify
paths for image/icon enums like we currently do in
`ui::components::icon`.

The icon component will get this same treatment in the future, once we:

- do the design work needed to standardize the icons
- remove unused icons
- update icon names

Release Notes:

- N/A

crates/ui/src/components/icon.rs

@@ -271,7 +271,6 @@ pub enum IconName {
     XCircle,
     ZedAssistant,
     ZedAssistantFilled,
-    ZedXCopilot,
     Visible,
 }
 
@@ -443,7 +442,6 @@ impl IconName {
             IconName::XCircle => "icons/error.svg",
             IconName::ZedAssistant => "icons/zed_assistant.svg",
             IconName::ZedAssistantFilled => "icons/zed_assistant_filled.svg",
-            IconName::ZedXCopilot => "icons/zed_x_copilot.svg",
             IconName::Visible => "icons/visible.svg",
         }
     }