Polyhedral: add hash method for Cone + Polyhedron

[benlorenz]

These have a custom == function, so they need a hash function (#2222).
We cannot reasonably hash the polytopes as we want to avoid triggering a convex hull computation. And even if we did, that would not give us a normal form that we could use for the hash. So we just hash the type and the ambient dimension.

Also add ambient_dim for LP and MILP.

x-ref: #2832

[codecov]

Codecov Report

Merging #2955 (4658ece) into master (4918a7a) will increase coverage by 0.00%.
Report is 3 commits behind head on master.
The diff coverage is 100.00%.

@@           Coverage Diff            @@
##           master    #2955    +/-   ##
========================================
  Coverage   80.34%   80.35%            
========================================
  Files         469      470     +1     
  Lines       66416    66659   +243     
========================================
+ Hits        53365    53566   +201     
- Misses      13051    13093    +42     

Files	Coverage Δ
src/PolyhedralGeometry/Cone/constructors.jl	89.13% <100.00%> (+1.03%)	⬆️
src/PolyhedralGeometry/Polyhedron/constructors.jl	93.61% <100.00%> (+0.59%)	⬆️
src/PolyhedralGeometry/linear_program.jl	92.72% <100.00%> (+0.13%)	⬆️
...PolyhedralGeometry/mixed_integer_linear_program.jl	57.14% <100.00%> (+0.69%)	⬆️

... and 14 files with indirect coverage changes