Switch QuantumCircuit.from_qasm_str and from_qasm_file to new parser

[jakelishman]

Summary

This uses the extensibility and the legacy compatiblity data in the new Rust OpenQASM 2 parser to switch over the old QuantumCircuit constructor methods to the new parser. This gives users of these methods large speedups while maintaining the same feature set (and fixing a long-standing bug surrounding U and CX!).

One test is removed for the circuit methods; the circuit methods are set to use strict=False mode of the new parser, which is more permissive, including making the empty string an allowable program. The alternative was to set strict=True, which would have made an unrelated test in SabreLayout fail instead due to its slightly improper use of floating-point values in OpenQASM 2 (the OQ2 spec technically requires decimal points even in constructs like 1e3, unlike other languages). Given that the previously OQ2 importer allowed these floats, it seemed safer to use strict=False mode, which is also generally more convenient for users.

The tests for the old paths are copied, to ensure they continue working during their potential deprecation and removal.

Details and comments

The new parser fixes several long-standing bugs/problems. Strictly we could have counted them as fixed since #9784 merged, but it's perhaps more complete to count them as fixed once the old interfaces use the new paths.

• Fix Improve qasm parsing times #7119: the new parser is much faster.
• Fix OpenQASM2 redo ANTLR Grammar -> AST -> QuantumCircuit #6089: the new parser builds QuantumCircuit directly, skipping DAGCircuit
• Fix Cannot build a circuit from qasm with an ecr gate #5536: the bug isn't present in the new parser
• Fix Factor out OpenQASM parser #1742: with the qiskit-qasm2 package available, the parser itself is factored out, though it doesn't build a reusable. We're not going to be supplying that, though.
• Fix Memory blowup when parsing a big qasm file #1168: the new parser never builds a complete internal AST or DAGCircuit, but streams a series of bytecode instructions on demand, so the intermediate memory usage is constant-sized rather than the old behaviour of being linear (with large constant factor).
• Fix QASM parser needs polishing #923: the old parser is not used, so this issue is obsoleted
• Fix Comments should be AST nodes #901: the new parser does not build an AST at all and comments do not have a place in QuantumCircuit, so this issue is at best obsolete.

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[coveralls]

Pull Request Test Coverage Report for Build 4691407246

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 25 unchanged lines in 5 files lost coverage.
• Overall coverage increased (+0.002%) to 85.743%

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Files with Coverage Reduction	New Missed Lines	%
qiskit/qasm/node/unaryoperator.py	2	70.59%
qiskit/qasm/node/prefix.py	3	52.17%
crates/accelerate/src/sabre_swap/layer.rs	4	97.32%
crates/qasm2/src/lex.rs	4	90.89%
crates/qasm2/src/parse.rs	12	97.11%

Totals
Change from base Build 4691279270:	0.002%
Covered Lines:	70116
Relevant Lines:	81775

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💛 - Coveralls

[jakelishman]

The error on Windows in this PR is fixed by #9958. It's arguably not really an error - OSError was also fine in that situation - but for the sake of the test suite having exactly equal behaviour (except for qasm2.loads("") no longer being an error), it's better to have the fix.

[kevinhartman]

This looks great! Good idea to keep testing the legacy importer path.