Add testing for Expr values through the transpiler pipelines

[jakelishman]

What should we add?

This is spiritually tracking the work labelled "PR 4" in the initial classical-expression design document.

On a scan through the transpiler passes, the only ones I could immediately see that look like they'll need attention are SabreLayout and SabreSwap, tracked in #10232, but since these don't support control-flow at all yet, there's no immediate issue yet.

This issue can be marked fixed once we've verified that there is support at all control-flow supported optimization_level settings through the transpiler (currently 0 and 1), and have added explicit tests to the suite that these expression values are correctly passed through transpile.