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Fix hash of `Parameter` and `ParameterExpression` (#10875)

* Fix hash of `Parameter` and `ParameterExpression`

This fixes the construction paths for `Parameter` and its hash such that
it will now correctly hash equal to any `ParameterExpression`s that it
compares equal to.  This is a requirement of the Python data model for
hashmaps and hashsets, which previously we were breaking.  In order to
achieve this, we slightly modify the hash key such that the `Parameter`
instances are no longer a part of the hash of `ParameterExpression`,
which means we can use the same hashing strategy for both.

This rearrangement has the benefit of removing the requirement for the
`__new__` overrides on `Parameter` and `ParameterVectorElement`.

* Add type hint

Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

* Tweak documentation wording

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Co-authored-by: Matthew Treinish <mtreinish@kortar.org>

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