added test coverage for task and function bodies being one statement

test/basic/tf_block.sv

+module top;
+    function [2:0] f;
+        input [2:0] n;
+        n += 1;
+        return n + 3;
+    endfunction
+    task t;
+        $display("hello");
+        $display("world");
+    endtask
+    initial t();
+    initial $display("f(0) = ", f(0));
+    initial $display("f(1) = ", f(1));
+endmodule

test/basic/tf_block.v

+module top;
+    function [2:0] f;
+        input [2:0] n;
+        f = n + 4;
+    endfunction
+    task t;
+        begin
+            $display("hello");
+            $display("world");
+        end
+    endtask
+    initial t();
+    initial $display("f(0) = ", f(0));
+    initial $display("f(1) = ", f(1));
+endmodule

test/basic/tf_block_tb.v

+// intentionally empty