test: add test cases for lexical scoping edge cases

Author: ryan-gang

test_programs/r4/3.lox

@@ -1,3 +1,18 @@
 ---
-expected_error_type: none
+expected_error_type: compile
 ---
+fun returnArg(arg) {
+  return arg;
+}
+
+var b = "global";
+
+{
+  var a = "first";
+  var b = returnArg(b); // Using global 'b' in its initializer, but through a function call
+  print b;
+}
+
+// Reassigning with self-reference is fine for globals
+var b = b + " updated";
+print b; 

test_programs/r4/4.lox

@@ -1,3 +1,15 @@
 ---
-expected_error_type: none
+expected_error_type: compile
 ---
+fun outer() {
+  var a = "outer";
+
+  fun inner() {
+    var a = a; // Error at 'a': Can't read local variable in its own initializer.
+    print a;
+  }
+
+  inner();
+}
+
+outer();