Include asset path in get_meta_path panic message (bevyengine#11504)

# Objective

- Fixes a hurdle encountered when debugging a panic caused by the file
watcher loading a `.gitignore` file, which was hard to debug because
there was no file name in the report, only `asset paths must have
extensions`

## Solution

- Panic with a formatted message that includes the asset path, e.g.
`missing expected extension for asset path .gitignore`

---------

Co-authored-by: Alice Cecile <[email protected]>
Co-authored-by: Doonv <[email protected]>

crates/bevy_asset/src/io/mod.rs

@@ -269,7 +269,7 @@ pub(crate) fn get_meta_path(path: &Path) -> PathBuf {
     let mut meta_path = path.to_path_buf();
     let mut extension = path
         .extension()
-        .expect("asset paths must have extensions")
+        .unwrap_or_else(|| panic!("missing extension for asset path {path:?}"))
         .to_os_string();
     extension.push(".meta");
     meta_path.set_extension(extension);