[ENH]: Add an easy way to plot an infinite half space (e.g. with a HalfSpace patch)

[carlosgmartin]

Problem

Using axhline, one can easily plot an infinite line:

def plot_line(ax, a, b, c, **kwargs):
    """Plots the solution to a x + b y = c."""
    ax.axline((c / a, 0), (0, c / b), **kwargs)

It would be nice to have an easy way to plot an infinite half space:

def plot_half_space(ax, a, b, c):
    """Plots the solution to a x + b y ≥ c."""
    ...

Proposed solution

This could potentially be done by adding a HalfSpace patch to matplotlib.patches.

For an analogue, see Mathematica's HalfSpace and HalfPlane.

[timhoffm]

This would be a reasonable feature. PRs welcome.