Closes #20853.

Some alternatives were suggested in the issue, namely disabling all checks, which is still an option but seems sub-optimal.

However, there are some implementation notes which are important.

This PR changes the behaviour of the python caller, which is now responsible for being the right size. That is:

subroutine foo(is_, ie_, arr, tout)
 implicit none
 integer :: is_,ie_
 real, intent(in) :: arr(is_:ie_)
 real, intent(out) :: tout(is_:ie_)
 tout = arr
end

After compiling f2py -m blah blah.f90, this can be called with:

import numpy as np
import blah
xlow = -6
xhigh = 4
xvec = np.arange(12)
def ubound(xl, xh):
  return abs(xl) + abs(xh) + 1
rval = blah.foo(is_ = xlow, ie_ xhigh,
         arr = xvec[:ubound(xlow, xhigh))
expval = np.arange(11, dtype = np.float32)
np.allclose(rval, expval) 

Essentially, the caller is now responsible in this scenario for ensuring that the size of the array passed in is correct, and this means for the most part that the slice should be calculated as above.