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

Cargo.lock

@@ -12273,6 +12273,7 @@ dependencies = [
  "story",
  "strum 0.25.0",
  "theme",
+ "ui_macros",
  "windows 0.58.0",
 ]
 
@@ -12287,6 +12288,16 @@ dependencies = [
  "ui",
 ]
 
+[[package]]
+name = "ui_macros"
+version = "0.1.0"
+dependencies = [
+ "convert_case 0.6.0",
+ "proc-macro2",
+ "quote",
+ "syn 1.0.109",
+]
+
 [[package]]
 name = "unicase"
 version = "2.7.0"