Add tests for nested with blocks

Added two tests that test the behavior of nested `with` blocks. When a
nested `with` block is started, using a variable referenced from the
enclosing one, expected behavior is to change the short-dot syntax scope
to the newly-referenced variable.

spec/inputs/with.moon

@@ -93,6 +93,16 @@ do
   with k.j = "jo"
     print \upper!
 
+do
+  with a
+    print .b
+    -- nested `with`s should change the scope correctly
+    with .c
+      print .d
 
-
+do
+  with a
+    -- nested `with`s with assignments should change the scope correctly
+    with .b = 2
+      print .c
 

spec/outputs/with.lua

@@ -131,6 +131,26 @@ do
     local _with_0 = "jo"
     k.j = _with_0
     print(_with_0:upper())
+  end
+end
+do
+  do
+    local _with_0 = a
+    print(_with_0.b)
+    do
+      local _with_1 = _with_0.c
+      print(_with_1.d)
+    end
+  end
+end
+do
+  do
+    local _with_0 = a
+    do
+      local _with_1 = 2
+      _with_0.b = _with_1
+      print(_with_1.c)
+    end
     return _with_0
   end
 end