FSC: Consider enabling `--parallelreferenceresolution` by default

https://github.com/dotnet/fsharp/pull/13521 introduces an FSC flag `--parallelreferenceresolution` that makes dll imports run in parallel.
I ran some tests and it gave 5% relative/600ms absolute speedup of single-project `dotnet build` for projects with lots of NuGet&project references.
Would it be possible to enable this feature by default?

If this were to be an opt-out feature, what would be the opt-out mechanism?

I believe parallel parsing is on by default and the only way to turn it off for end-users is via the `OtherFlags` MSBuild property.