Allow naming space view containers

[abey79]

What

As the title say ☝🏻

Decisions:

• Keep "Viewport" in the name of the root container (see screenshot below).
• Refactor some stuff:
  • moved Contents to re_viewer_contex (I actually been meaning to do that for a while but can't remember why now)
  • moved/renamed SpaceViewName to ContentsName in re_viewer_context

⚠️ review commit by commit

container-names.mp4

import rerun as rr
import rerun.blueprint as rrb

rr.init(
    "rerun_example_demo",
    blueprint=rrb.Horizontal(
        rrb.Vertical(
            rrb.Spatial3DView(origin="/point3d"),
            rrb.Spatial3DView(origin="/point3d"),
            name="First Vertical",
        ),
        rrb.Vertical(
            rrb.Spatial3DView(origin="/point3d"),
            rrb.Spatial3DView(origin="/point3d"),
            name="Second Vertical",
        ),
        name="Top-Level",
    ),
)
rr.connect()

rr.log("point3d", rr.Points3D([0, 1, 2]))

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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Size changes

Name	main	5626/merge	Change
rrt-star.rrd	5.77 MiB	1.60 MiB	-72.27%