Context menu 3: add "Move to new container" context menu action

[abey79]

What

• Follow-up to Context menu 2: add support for multiple selection #5205
• Part of Add contextual menu to blueprint tree for common actions #4823

This PR adds a new "Move to new container" context menu action, that applies when one or more space views and/or containers are selected. The new container is created at the location of the clicked item, and all the selected items are moved into it.

Note: one very often runs into this while using this feature:

• Improve how collapsed state is saved for space views, containers, and DataResults in the Blueprint Tree UI #5208

TODO in future PR:

• additional actions
• entity level manipulations
• use ListItem instead of label/WidgetText
• better folder structure
• release checklist update

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using newly built examples: app.rerun.io
  • Using examples from latest main build: app.rerun.io
  • Using full set of examples from nightly build: app.rerun.io
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!

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[teh-cmc]

It might be a bit weird that this interaction shows up even when the multi-selection includes the viewport itself:

It doesn't actually applies to it if you go through with it so it's not the end of the world, just weird.

[teh-cmc]

It is a bit weird that the context menu shows options that will end up doing nothing (e.g. Move to horizontal when you're already in an horizontal container); but again not the end of the world.

[abey79]

It might be a bit weird that this interaction shows up even when the multi-selection includes the viewport itself

Yeah, that's a matter of choice. The alternative I considered is to disable entirely the context menu whenever the selection is "root container + something", because none of the operations that applies to multiple hierarchy thing can be applied to the root container (visibility, remove, move to new container).

None of these seem ideal to me though.

[teh-cmc]

Once again discovered many things I didn't know about 🤯

[abey79]

It is a bit weird that the context menu shows options that will end up doing nothing (e.g. Move to horizontal when you're already in an horizontal container); but again not the end of the world.

Two issues there:

• I forgot to exclude horizontal-in-horizontal (and V-in-V) options, which doesn't make sense 🤦🏻. Will fix.
• We still have some simplification of the hierarchy that kicks in in a disruptive was sometimes. I still have to track that, but it's a wider issue (ie. affect all creation of containers, not only through context menu.