Add regression test for is_object_safe field on traits

Author: GuillaumeGomez

tests/rustdoc-json/traits/is_object_safe.rs

@@ -0,0 +1,19 @@
+#![no_std]
+
+// @has "$.index[*][?(@.name=='FooUnsafe')]"
+// @has "$.index[*][?(@.name=='FooUnsafe')].inner.trait.is_object_safe" false
+pub trait FooUnsafe {
+    fn foo() -> Self;
+}
+
+// @has "$.index[*][?(@.name=='BarUnsafe')]"
+// @has "$.index[*][?(@.name=='BarUnsafe')].inner.trait.is_object_safe" false
+pub trait BarUnsafe<T> {
+    fn foo(i: T);
+}
+
+// @has "$.index[*][?(@.name=='FooSafe')]"
+// @has "$.index[*][?(@.name=='FooSafe')].inner.trait.is_object_safe" true
+pub trait FooSafe {
+    fn foo(&self);
+}