Fix negation of public input in assert_equal_public_point

[moCello]

Describe what you want implemented
When asserting that a point is equal a public point in-circuit, the coordinates of the public point are appended to the circuit is their negative form while they should be positive.

The fix requires to change append_equal_constant to append the constant in it's positive form as well.

Describe "Why" this is needed
Appending public inputs negatively is confusing and can lead to the verifier rejecting a perfectly fine proof simply because the verifier expected the public inputs to be positive.

Describe alternatives you've considered
N/A

Additional context
see issue #717