function(SetExpr(...)) could be handled better

[smichr]

from #14251, when SetExpr is the argument of a function it is handled less gracefully than when the argument is AccumBounds:

>>> cos(AccumBounds(-1, 2))
AccumBounds(cos(2), 1)
>>> cos(SetExpr(Interval(-1, 2)))
SetExpr(ImageSet(Lambda(x, cos(x)), Interval(-1, 2)))
>>> var('a b', real=True)
>>> sin(AccumBounds(a, b))
TypeError: input failed to evaluate
>>> sin(SetExpr(Interval(a, b)))
SetExpr(ImageSet(Lambda(x, sin(x)), Interval(a, b)))

[oscarbenjamin]

I'm not sure how to relate SetExpr and ImageSet because they don't quite do the same thing:

In [28]: s = Interval(0, 1)

In [29]: se = SetExpr(s)

In [30]: se**2 - se
Out[30]: SetExpr([-1, 1])

In [31]: ImageSet(Lambda(x, x**2 - x), s)
Out[31]: 
⎧ 2     │           ⎫
⎨x  - x │ x ∊ [0, 1]⎬
⎩       │           ⎭

In [32]: ImageSet(Lambda(x, x**2 - x), s).doit()
Out[32]: [-1/4, 0]