Fix quadrature rule hash

[connorjward]

Also remove some uses of deprecated @abstractproperty and gives cells and point sets repr()s.

Necessary for firedrakeproject/firedrake#3989

[connorjward]

@ksagiyam please can you take a look at this too?

[ksagiyam]

This PR itself looks almost fine to me, but floats being used in some __repr__() could cause issues in computing cache key in firedrake.tsfc_interface.

[connorjward]

but floats being used in some repr() could cause issues in computing cache key in firedrake.tsfc_interface.

An excellent catch. I will think on that.

[connorjward]

This PR itself looks almost fine to me, but floats being used in some repr() could cause issues in computing cache key in firedrake.tsfc_interface.

I have now had a stab at fixing this. UFL provides a format_float function that it uses for this purpose in constantvalue.py.