coverage: Add a test for #[coverage(..)] on closures

tests/coverage/coverage_attr_closure.rs

@@ -0,0 +1,42 @@
+#![feature(coverage_attribute, stmt_expr_attributes)]
+#![allow(dead_code)]
+// edition: 2021
+
+static GLOBAL_CLOSURE_ON: fn(&str) = #[coverage(on)]
+|input: &str| {
+    println!("{input}");
+};
+static GLOBAL_CLOSURE_OFF: fn(&str) = #[coverage(off)]
+|input: &str| {
+    println!("{input}");
+};
+
+#[coverage(on)]
+fn contains_closures_on() {
+    let _local_closure_on = #[coverage(on)]
+    |input: &str| {
+        println!("{input}");
+    };
+    let _local_closure_off = #[coverage(off)]
+    |input: &str| {
+        println!("{input}");
+    };
+}
+
+#[coverage(off)]
+fn contains_closures_off() {
+    let _local_closure_on = #[coverage(on)]
+    |input: &str| {
+        println!("{input}");
+    };
+    let _local_closure_off = #[coverage(off)]
+    |input: &str| {
+        println!("{input}");
+    };
+}
+
+#[coverage(off)]
+fn main() {
+    contains_closures_on();
+    contains_closures_off();
+}