Add tags to UiStack - #4617

### What

When #6491 migrated to using `UiStack` for full span scopes, it wasn't
possible to manually set a full span scope somewhere. Because of that, a
clip rect hack was used for the streams tree. With
emilk/egui#4617, it's now possible to support
that correctly, so this PR introduces `UiExt::full_span_scope()` and
uses it for the streams tree.

This PR also bumps the egui/egui_commonmark/egui_tiles commits.

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested the web demo (if applicable):
* Using examples from latest `main` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/{{pr.number}}?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[rerun.io/viewer](https://rerun.io/viewer/pr/{{pr.number}}?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG
* [x] If applicable, add a new check to the [release
checklist](https://github.com/rerun-io/rerun/blob/main/tests/python/release_checklist)!

- [PR Build Summary](https://build.rerun.io/pr/{{pr.number}})
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
- [Wasm size tracking](https://build.rerun.io/graphs/sizes.html)

To run all checks from `main`, comment on the PR with `@rerun-bot
full-check`.

You can now set custom tags on the `UiStack`. This allows you to write
code that is situationally aware at runtime. For instance, you could
decide wether or not a label should truncate its text depending on what
part of your ui it is in, without having to pass that info down via the
callstack.