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.toml

@@ -118,6 +118,7 @@ members = [
     "crates/title_bar",
     "crates/ui",
     "crates/ui_input",
+    "crates/ui_macros",
     "crates/util",
     "crates/vcs_menu",
     "crates/vim",
@@ -292,6 +293,7 @@ time_format = { path = "crates/time_format" }
 title_bar = { path = "crates/title_bar" }
 ui = { path = "crates/ui" }
 ui_input = { path = "crates/ui_input" }
+ui_macros = { path = "crates/ui_macros" }
 util = { path = "crates/util" }
 vcs_menu = { path = "crates/vcs_menu" }
 vim = { path = "crates/vim" }
@@ -333,6 +335,7 @@ chrono = { version = "0.4", features = ["serde"] }
 clap = { version = "4.4", features = ["derive"] }
 clickhouse = "0.11.6"
 cocoa = "0.26"
+convert_case = "0.6.0"
 core-foundation = "0.9.3"
 core-foundation-sys = "0.8.6"
 ctor = "0.2.6"