fix: compiling on windows requires cosmic-icons in project root

* fix: compiling on windows requires cosmic-icons in project root

crabtime provides crabtime::WORKSPACE_PATH to refer to the
CARGO_MANIFEST_DIR of the top level crate being built, which means when
building libcosmic directly, crabtime::WORKSPACE_PATH will work, but
when building it as a dependency of another crate,
crabtime::WORKSPACE_PATH will no longer refer to the path to libcosmic.

I don't think there's a good workaround, since when in the context of
crabtime, CARGO_MANIFEST_DIR refers to the path to the crate generated
by crabtime rather than to libcosmic.

This replaces crabtime with a simple build.rs script that generates a
file in OUT_DIR.

* fix: do not generate icon bundle for unix targets

---------

Co-authored-by: Michael Aaron Murphy <michael@mmurphy.dev>

build.rs

@@ -0,0 +1,56 @@
+fn main() {
+    println!("cargo::rerun-if-changed=build.rs");
+
+    #[cfg(not(unix))]
+    generate_bundled_icons();
+}
+
+#[cfg(not(unix))]
+fn generate_bundled_icons() {
+    println!("cargo::rerun-if-changed=cosmic-icons");
+
+    let manifest_dir = std::path::Path::new(std::env!("CARGO_MANIFEST_DIR"));
+    let icon_paths = [
+        "cosmic-icons/freedesktop/scalable",
+        "cosmic-icons/extra/scalable",
+    ];
+
+    let key_value_assignments = icon_paths
+        .into_iter()
+        .map(|path| manifest_dir.join(path))
+        .inspect(|icon_path| assert!(icon_path.exists(), "path = {icon_path:?}"))
+        .map(|icon_path| std::fs::read_dir(icon_path).unwrap())
+        .flat_map(|dir| {
+            dir.flat_map(|entry| entry.unwrap().path().read_dir().unwrap())
+                .map(|entry| {
+                    let entry = entry.unwrap();
+                    let path = entry.path().canonicalize().unwrap();
+                    let file_name = path.file_stem().unwrap().to_str().unwrap().to_owned();
+                    let path = path.into_os_string().into_string().unwrap();
+                    (file_name, path)
+                })
+        })
+        .fold(
+            std::collections::BTreeMap::new(),
+            |mut set, (name, path)| {
+                set.insert(name, path);
+                set
+            },
+        )
+        .into_iter()
+        .fold(String::new(), |mut output, (name, path)| {
+            output.push_str(&format!("    \"{name}\" => include_bytes!(\"{path}\"),\n"));
+            output
+        });
+
+    let code = [
+        "static ICONS: phf::Map<&'static str, &'static [u8]> = phf::phf_map!(\n",
+        &key_value_assignments,
+        ");",
+    ]
+    .concat();
+
+    let out_dir = std::env::var_os("OUT_DIR").unwrap();
+    let out_file = std::path::Path::new(&out_dir).join("bundled_icons.rs");
+    std::fs::write(&out_file, &code).unwrap();
+}