Rework loading images from files (#7088)

This PR is a follow-up to #7084, where I noted that I wasn't satisfied
with using `SharedUri` to represent both URIs and paths on the local
filesystem:

> I'm still not entirely happy with this naming, as the file paths that
we can store in here are not _really_ URIs, as they are lacking a
protocol.
>
> I want to explore changing `SharedUri` / `SharedUrl` back to alway
storing a URL and treat local filepaths differently, as it seems we're
conflating two different concerns under the same umbrella, at the
moment.

`SharedUri` has now been reverted to just containing a `SharedString`
with a URI.

`ImageSource` now has a new `File` variant that is used to load an image
from a `PathBuf`.

Release Notes:

- N/A

crates/gpui/src/shared_uri.rs

@@ -1,65 +1,25 @@
-use std::ops::{Deref, DerefMut};
+use derive_more::{Deref, DerefMut};
 
 use crate::SharedString;
 
-/// A URI stored in a [`SharedString`].
-#[derive(PartialEq, Eq, Hash, Clone)]
-pub enum SharedUri {
-    /// A path to a local file.
-    File(SharedString),
-    /// A URL to a remote resource.
-    Network(SharedString),
-}
-
-impl SharedUri {
-    /// Creates a [`SharedUri`] pointing to a local file.
-    pub fn file<S: Into<SharedString>>(s: S) -> Self {
-        Self::File(s.into())
-    }
-
-    /// Creates a [`SharedUri`] pointing to a remote resource.
-    pub fn network<S: Into<SharedString>>(s: S) -> Self {
-        Self::Network(s.into())
-    }
-}
-
-impl Default for SharedUri {
-    fn default() -> Self {
-        Self::Network(SharedString::default())
-    }
-}
-
-impl Deref for SharedUri {
-    type Target = SharedString;
-
-    fn deref(&self) -> &Self::Target {
-        match self {
-            Self::File(s) => s,
-            Self::Network(s) => s,
-        }
-    }
-}
-
-impl DerefMut for SharedUri {
-    fn deref_mut(&mut self) -> &mut Self::Target {
-        match self {
-            Self::File(s) => s,
-            Self::Network(s) => s,
-        }
-    }
-}
+/// A [`SharedString`] containing a URI.
+#[derive(Deref, DerefMut, Default, PartialEq, Eq, Hash, Clone)]
+pub struct SharedUri(SharedString);
 
 impl std::fmt::Debug for SharedUri {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Self::File(s) => write!(f, "File({:?})", s),
-            Self::Network(s) => write!(f, "Network({:?})", s),
-        }
+        self.0.fmt(f)
     }
 }
 
 impl std::fmt::Display for SharedUri {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{}", self.as_ref())
+        write!(f, "{}", self.0.as_ref())
+    }
+}
+
+impl<T: Into<SharedString>> From<T> for SharedUri {
+    fn from(value: T) -> Self {
+        Self(value.into())
     }
 }