Implement fallback priorities and han unification on Unix

examples/text/src/font/fallback/macos.rs

@@ -0,0 +1,11 @@
+use unicode_script::Script;
+
+// Fallbacks to use after any script specific fallbacks
+pub fn common_fallback() -> &'static [&'static str] {
+    &[]
+}
+
+// Fallbacks to use per script
+pub fn script_fallback(script: &Script, locale: &str) -> &'static [&'static str] {
+    &[]
+}