Better mechanism to control SetterFlags

[PMeira]

Currently this is an advanced feature, and users need to leave the comfort of the Python properties, using instead the setter methods in order to pass both a value and the flags.

Some context, from the tests:

    alt.Clear()
    ls = alt.LoadShape.new('test_shape')
    with pt.raises(DSSException):
        ls.PMult = [1.0, 2.0, 3.0]

    ls._set_PMult([1.0, 2.0, 3.0], SetterFlags.ImplicitSizes)
    assert tuple(ls.PMult) == (1.0, 2.0, 3.0)

    ls.end_edit()

Some possible alternatives:

• Use a context manager in Python to keep the flags used in a block, use these flags on each Python function (when passing to the C API) and reset them later. This could be combined with the Edit context manager later.

with alt.with_setter_flags(SetterFlags.ImplicitSizes):
    ls = alt.LoadShape.new('test_shape')
    ls.PMult = [1.0, 2.0, 3.0]
    assert tuple(ls.PMult) == (1.0, 2.0, 3.0)
    ls.end_edit()

• Introduce a pair of API functions to control some default flags, expose it as a property. For this, we wouldn't need to change much of the Python code, but would require consuming the default flags on the engine:

    alt.DefaultSetterFlags = SetterFlags.ImplicitSizes
#...
    ls = alt.LoadShape.new('test_shape')
    ls.PMult = [1.0, 2.0, 3.0]
    assert tuple(ls.PMult) == (1.0, 2.0, 3.0)
    ls.end_edit()

Other examples include using SetterFlags.AvoidFullRecalc to minimize Yprim and SystemY changes for loads and generators. This is valid for both individual and batch operations.