Add max_trials parameter to VF2PostLayout.

[kevinhartman]

Summary

Adds a new parameter max_trials to pass VF2PostLayout which, when specified, limits the number of layouts discovered and compared when searching for the best layout.

This can be used to place an upper bound on the time spent scoring potential layouts, which may be useful for larger devices. In a follow-up PR, we'll specify the parameter accordingly when invoking VF2 post layout within the preset pass managers.

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[mtreinish]

I've tagged this as being part of the 0.24.0 as a feature freeze exception. This extra flag for VF2PostLayout is a prerequisite for fixing #9834. #9834 is a potential blocker for supporting some near future devices so we've decided it was a final release (not rc1) blocker to fix the issue. But, since we since we need this flag to be able to set limits in vf2postlayout to avoid the issue this needs to be included as part of RC1 even though it's coming in a week late. If there is any disagreement with this we can untag this from the release and discuss further.

[coveralls]

Pull Request Test Coverage Report for Build 4694176989

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 34 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+0.03%) to 85.798%

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Files with Coverage Reduction	New Missed Lines	%
qiskit/transpiler/passes/routing/sabre_swap.py	1	95.24%
crates/qasm2/src/lex.rs	5	90.63%
crates/qasm2/src/parse.rs	6	97.58%
qiskit/transpiler/passes/layout/sabre_layout.py	22	75.48%

Totals
Change from base Build 4692324070:	0.03%
Covered Lines:	70453
Relevant Lines:	82115

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💛 - Coveralls

[mtreinish]

The release note LGTM, just one small inline comment. After that I think we're good to merge this.

[mtreinish]

LGTM, thanks for the quick updates.