This commit adds a new transpiler pass MinimumPoint which is used to
find a local minimum point from the property set between executions of
the pass. This is similar to the existing FixedPoint pass but will find
the minimum fixed point over the past n exeuctions as opposed to finding
a when two subsequent exectuions are at the same point. This is then
used in optimization level 3 because the 2q unitary synthesis
optimization that is part of the optimization loop can occasionally get
stuck oscillating between multiple different equivalent decompositions
which prevents the fixed point condition from ever being reached. By
checking that we've reached the minimum over the last 5 executions we
ensure we're reaching an exit condition in this situation.

Fixes Qiskit#5832
Fixes Qiskit#9177

(the underlying cause of the optimization loop's inability to converge
at optimization level 3 is not fixed here, there is still a root cause
of instability in UnitarySynthesis this just changes the loop exit
condition so we're never stuck in an infinte loop)

This commit reworks the logic of the pass to track the state via a
dataclass instead of using separate property set fields. This cleans up
the code for dealing with checking the current state relative to earlier
iterations by making the access just attributes instead of secret
strings. At the same time the tests were updated to handle this new data
structure comments were added to better explain the logic flow being
tested.

Co-authored-by: Jake Lishman <[email protected]>