BUG: restricted mode in Lineareigenproblem for mixed problems.

[karimnorouzi]

Restricted mode can not create restricted function space for mixed problems involving vectors

here is the code to reproduce the problem

from firedrake import *
mesh = UnitSquareMesh(32, 32)

left, right, bottom, top = 1, 2, 3, 4
V = VectorFunctionSpace(mesh, "CG", 2)
P = FunctionSpace(mesh, "CG", 1)
Z = V*P
z = TrialFunctions(Z)
u, p = z
dz = TestFunctions(Z)
du, dp = dz
mu = 1e1
eps = lambda u:0.5*(grad(u) + grad(u).T)

A = (2*mu*inner(eps(u), eps(du)) - dp*div(u) - p*div(du))*dx
M = (inner(u, du) + p*dp)*dx

bcs = [
       DirichletBC(Z.sub(0).sub(0), Constant(0), (left, right)),
       DirichletBC(Z.sub(0).sub(1), Constant(0), (bottom)),
       ]

opts = {"eps_gen_non_hermitian": None,
        "eps_largest_imaginary": None,
        "st_type": "shift",
        "eps_target": None,
        "st_pc_factor_shift_type": "NONZERO"}
n = 5
problem = LinearEigenproblem(A = A, M = M, bcs = bcs, restrict = True)
eigensolver = LinearEigensolver(problem, n_evals=5, solver_parameters= opts)
nconv = eigensolver.solve()

Error message
File ".../firedrake/src/firedrake/firedrake/functionspaceimpl.py", line 476, in init
raise ValueError("Can't create FunctionSpace for MixedElement")

ValueError: Can't create FunctionSpace for MixedElement