feat(log): implement mobile logging

plugins/log/build.rs

@@ -0,0 +1,12 @@
+fn alias(alias: &str, has_feature: bool) {
+    if has_feature {
+        println!("cargo:rustc-cfg={alias}");
+    }
+}
+
+fn main() {
+    let target_os = std::env::var("CARGO_CFG_TARGET_OS").unwrap();
+    let mobile = target_os == "ios" || target_os == "android";
+    alias("desktop", !mobile);
+    alias("mobile", mobile);
+}