Add ui_macros crate & DerivePathStr derive macro (#17811)

This PR adds the `ui_macros` crate to allow building supporting macros
for the `ui` crate.

Additionally, it implements the `DerivePathStr` derive macro and the
`path_str` attribute macro. These macros work together to generate a
`path` method for enum variants, which is useful for creating
standardized string representations of enum variants.

The `DerivePathStr` macro provides the following functionality:
- Generates a `path` method for each enum variant.
- Allows specifying a prefix (required) and suffix (optional) for all
paths.
- Supports `strum` attributes for case conversion (e.g., snake_case,
lowercase).

Usage example:

```rust
#[derive(DerivePathStr)]
#[path_str(prefix = "my_prefix", suffix = ".txt")]
#[strum(serialize_all = "snake_case")]
enum MyEnum {
    VariantOne,
    VariantTwo,
}

// Generated paths:
// MyEnum::VariantOne.path() -> "my_prefix/variant_one.txt"
// MyEnum::VariantTwo.path() -> "my_prefix/variant_two.txt"
```

In a later PR this will be used to automate the creation of icon & image
paths in the `ui` crate.

This gives the following benefits:

1. Ensures standard naming of assets as paths are not manually
specified.
2. Makes adding new enum variants less tedious and error-prone.
3. Quickly catches missing or incorrect paths during compilation.
3. Adds a building block towards being able to lint for unused assets in
the future.

Release Notes:

- N/A

crates/ui/src/path_str.rs

@@ -0,0 +1,33 @@
+#[cfg(test)]
+mod tests {
+    use strum::EnumString;
+    use ui_macros::{path_str, DerivePathStr};
+
+    #[test]
+    fn test_derive_path_str_with_prefix() {
+        #[derive(Debug, EnumString, DerivePathStr)]
+        #[strum(serialize_all = "snake_case")]
+        #[path_str(prefix = "test_prefix")]
+        enum MyEnum {
+            FooBar,
+            Baz,
+        }
+
+        assert_eq!(MyEnum::FooBar.path(), "test_prefix/foo_bar");
+        assert_eq!(MyEnum::Baz.path(), "test_prefix/baz");
+    }
+
+    #[test]
+    fn test_derive_path_str_with_prefix_and_suffix() {
+        #[derive(Debug, EnumString, DerivePathStr)]
+        #[strum(serialize_all = "snake_case")]
+        #[path_str(prefix = "test_prefix", suffix = ".txt")]
+        enum MyEnum {
+            FooBar,
+            Baz,
+        }
+
+        assert_eq!(MyEnum::FooBar.path(), "test_prefix/foo_bar.txt");
+        assert_eq!(MyEnum::Baz.path(), "test_prefix/baz.txt");
+    }
+}

crates/ui/src/ui.rs

@@ -8,6 +8,7 @@ mod components;
 mod disableable;
 mod fixed;
 mod key_bindings;
+mod path_str;
 pub mod prelude;
 mod selectable;
 mod styled_ext;