[tests] Add more Null op tests

[yuxiaomao]

When I made the HL implementation for null ops, I found that we can have some more spec tests

• when doing </>/<=/>= between null values: it does not really make sens but I think it's good to ensure the same behavior
• between null : Null<Int> and 0 : Null<Int>: it's different than Null<Int> with Int, at least the code generated by HL is different

It seems work as expected on HL, let's see if tests pass for other target.

[yuxiaomao]

In summary:

Cpp fail because when comparing null <= null, it convert the value to 0 first (I don't think it's really a problem by itself).

Php fail because I added analyzer(ignore) on testOps. Probably the assign does not worked:

var k = false;
f((k = true) ? false : true);
t(k);

Lua: I can't understand the error 😢