Enhance the ParsedValue.value setter to correctly update object attributes

[paul356]

Sometimes we may want to add a new attribute to a node by assign a sexpdata tree to .value. But the fields are not updated according to the new value. For example _value and children is not updated which may causes problem if further operations depend on these fields.

This enhancement is to enhance the ParsedValue.value setter to update the fields according to assignee. I have verified the new function by adding a hide = yes attribute to a property string. The test code is like.

sch.symbol.C70.property.LCSC_Part__.effects.value = [[Symbol('font'), [Symbol('size'), 1.27, 1.27]], [Symbol('hide'), Symbol('yes')]]
OVERWRITING font
sch.symbol.C70.property.LCSC_Part__.effects
<effects [font = [<size [1.27, 1.27]>], hide = True]>
sch.symbol.C70.property.LCSC_Part__.effects.tree
[Symbol('effects'), [Symbol('font'), [Symbol('size'), 1.27, 1.27]], [Symbol('hide'), Symbol('yes')]]
sch.symbol.C70.property.LCSC_Part_.effects.value
sch.symbol.C70.property.LCSC_Part_.effects.font
font = [<size [1.27, 1.27]>]
sch.symbol.C70.property.LCSC_Part__.effects.hide
hide = True

[paul356]

@psychogenic Hi Pat. Do you have time to review this enhancement?