Revert "Revert 0.7.6 code for 0.7.5 re-release"

This reverts commit d1349c9cfb.

test/test_suite/compile_time_introspection/defined_subscript_assign.c3

@@ -0,0 +1,14 @@
+fn int main(String[] args)
+{
+	MyArray a = {{1, 4, 3, 6, 5}};
+	$assert(!$defined(a[0] = 2));
+	return 0;
+}
+
+struct MyArray
+{
+	int[] val;
+}
+
+fn int MyArray.get(self, usz idx) @operator([]) => self.val[idx];
+fn usz MyArray.len(self) @operator(len) => self.val.len;