Add a way to do shallow equal

Possible names for a shallow eq validator:

• toShallowEqual
• toBe (jest style)

Personally I like toShallowEqual - it also goes well with toLooseEqual that we already have.

[krzkaczor]

As per discussion with @sz-piotr I decided to rename it to toStrictlyEqual.

IMO toBe is too short it looks like it’s incentivizing by us to use but in reality, 95% of cases should be covered by toEqual. I will fix it and merge it later today.

[krzkaczor]

@sz-piotr So what you’re saying is that we shouldn’t allow (at least on a type system lvl) comparing primitive values with toBe, right?

It’s an interesting point… and I think you’re right. But! We can make a signature to be more like: toBe(value: T) and add condition that T extends object. This way we get type safety.