Write some more scope edge case tests.

test/variable/global_in_initializer.wren

@@ -0,0 +1,2 @@
+var a = a == null
+io.write(a) // expect: true

test/variable/local_in_initializer.wren

@@ -0,0 +1,5 @@
+// skip: Variables should not be in scope in their initializer.
+{
+  var a = a + 1 // expect error
+  io.write(a)
+}

test/variable/shadow_and_local.wren

@@ -0,0 +1,8 @@
+{
+  var a = "outer"
+  {
+    io.write(a) // expect: outer
+    var a = "inner"
+    io.write(a) // expect: inner
+  }
+}

test/variable/shadow_in_initializer.wren

@@ -0,0 +1,11 @@
+// skip: Variables should not be in scope in their initializer.
+{
+  var a = "outer"
+  {
+    var a = a + " inner"
+    io.write(a) // expect: outer inner
+  }
+}
+
+// TODO: Test referring to class name inside class for class at global scope
+// and in local scope.