Tree widget: Replace usages of `InVirtualSet` with `IdSet` virtual table

[grigasp]

As described in https://www.itwinjs.org/learning/ecsqlreference/idset/#idset-virtual-table, IdSet virtual table should be a more performant version of the InVirtualSet function. Also, it's pretty much a direct replacement, so migration should be straightforward.

While it's still marked "experimental", @khanaffan confirms it's safe to use.

So I'm saying we should migrate to IdSet ASAP on tree-widget/next branch.

[khanaffan]

We will remove the experimental tag once we see it working as intended. And for that it be nice if you can share any performance improvement that you get out of it.

[grigasp]

We will remove the experimental tag once we see it working as intended. And for that it be nice if you can share any performance improvement that you get out of it.

@JonasDov started working on the update. Hooefully the performance benchmark tests that we have for tree widget will show an improvement.

[JonasDov]

After trying to migrate, found that multiple IdSet can't be used in a single query. Filled an issue in itwinjs-core. Will be continuing after it completes.