[Op] Add an operator for comparing shape values

[slyubomirsky]

This PR adds an operator called shape_equals that, as the name suggests, compares two shapes and returns a bool indicating whether they are equal. This will allow for comparing shapes within Relax without using a PackedFunc.

CC @mbaret

[slyubomirsky]

@mbaret recommended it for dynamically inspecting shapes. Perhaps he can give more specifics?

[tqchen]

Note, this PR should likely be part of PRs to send to unity branch