### What
This is so we can test things out before the next release, and also get
in some new egui features for the plot aggregator and drag-and-drop.

* Closes #4716
* Closes #4794

### TODO
* [x] Fix hovering ListItems in blueprint panel

### wgpu changelog
https://github.com/gfx-rs/wgpu/blob/trunk/CHANGELOG.md#v0190-2024-01-17

### relevant egui changelog (so far)

#### eframe
* Keep `ViewportInfo::maximized` and `minimized` up-to-date on Windows
[#3831](emilk/egui#3831) (thanks
[@rustbasic](https://github.com/rustbasic)!)
* Update wgpu to 0.19 [#3824](emilk/egui#3824)
* Fix: handle `IconData::default()` without crashing
[#3842](emilk/egui#3842)

#### egui_extras
* Fix unwraps in SVG scaling
[#3826](emilk/egui#3826) (thanks
[@amPerl](https://github.com/amPerl)!)
* Update to ehttp 0.4 [#3834](emilk/egui#3834)

#### egui_plot
* Make `egui_plot::PlotMemory` public
[#3871](emilk/egui#3871)

#### egui
* Selectable text in Labels
[#3814](emilk/egui#3814)
* `ComboBox`: add builder method for height
[#3001](emilk/egui#3001) (thanks
[@hinto-janai](https://github.com/hinto-janai)!)
* Add keys `?`, `/`, `|`
[#3820](emilk/egui#3820)
* Fix clickable widgets blocking scrolling on touch screens
[#3815](emilk/egui#3815) (thanks
[@lucasmerlin](https://github.com/lucasmerlin)!)
* Fix `stable_dt` [#3832](emilk/egui#3832)
* Bug Fix : `Response::is_pointer_button_down_on` is now false the frame
the button is released [#3833](emilk/egui#3833)
(thanks [@rustbasic](https://github.com/rustbasic)!)
* Use runtime knowledge of OS for OS-specific text editing
[#3840](emilk/egui#3840)
* Refactor: move text selection logic to own module
[#3843](emilk/egui#3843)
* Fix: dragging to above/below a `TextEdit` or `Label` will select text
to begin/end [#3858](emilk/egui#3858)
* Add `Response::contains_pointer`
[#3859](emilk/egui#3859)
* Always set `response.hovered` to false when dragging another widget
[#3860](emilk/egui#3860)
* Add `Align2::anchor_size`
[#3863](emilk/egui#3863)
* Add `Context::debug_text`
[#3864](emilk/egui#3864)

#### epaint
* Add `Align2::anchor_size`
[#3863](emilk/egui#3863)

### 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 newly built examples:
[app.rerun.io](https://app.rerun.io/pr/4885/index.html)
* Using examples from latest `main` build:
[app.rerun.io](https://app.rerun.io/pr/4885/index.html?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[app.rerun.io](https://app.rerun.io/pr/4885/index.html?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

- [PR Build Summary](https://build.rerun.io/pr/4885)
- [Docs
preview](https://rerun.io/preview/eb1bce846c3adb29b99d04018b002475994ad213/docs)
<!--DOCS-PREVIEW-->
- [Examples
preview](https://rerun.io/preview/eb1bce846c3adb29b99d04018b002475994ad213/examples)
<!--EXAMPLES-PREVIEW-->
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
- [Wasm size tracking](https://build.rerun.io/graphs/sizes.html)

---------

Co-authored-by: Andreas Reich <r_andreas2@web.de>

### What

This PR implements a couple of single-selection drag-and-drop demo with
`ListItem`s in `re_ui_example`. One is flat, the other is hierarchical.
Most of it happens in `re_ui_example`, with some minimal support for
draggability in `ListItem`. The goal is to identify proper patterns (and
egui TODOs) for drag-and-drop support in the blueprint tree UI.

TODO:
- [x] iron out some bug where items disappear
- [x] highlight destination container
- [x] ascii art documentation for the drag areas
- [x] apply any change from:
    - emilk/egui#3859
    - emilk/egui#3860


https://github.com/rerun-io/rerun/assets/49431240/54588326-7e69-4d38-b16d-da17fc88b6b7

Contributes towards:
- #2652 

### 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 newly built examples:
[app.rerun.io](https://app.rerun.io/pr/4879/index.html)
* Using examples from latest `main` build:
[app.rerun.io](https://app.rerun.io/pr/4879/index.html?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[app.rerun.io](https://app.rerun.io/pr/4879/index.html?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

- [PR Build Summary](https://build.rerun.io/pr/4879)
- [Docs
preview](https://rerun.io/preview/94b9a81e7d5b2934b44919453ce2c92257b46a73/docs)
<!--DOCS-PREVIEW-->
- [Examples
preview](https://rerun.io/preview/94b9a81e7d5b2934b44919453ce2c92257b46a73/examples)
<!--EXAMPLES-PREVIEW-->
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
- [Wasm size tracking](https://build.rerun.io/graphs/sizes.html)

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>