Consistent open/import/log_file behaviors in all common scenarios

[teh-cmc]

All the major data-loading paths now behave sanely and consistently on both native and web.

You can try and look at the matrix below for the specific behavior of each path, but really my advice would be to just play with it to get a sense of things.

One of these days we'll clearly need a bottom-up in-hindsight refactoring for all these things, it is so complex.
But today is not that day.

• Fixes Inconsistent drag-and-drop behavior: dropping multiple files results in multiple recordings #7965

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Checklist:

• Native:
  • Open:
    • In welcome screen:
      • Single file (new app, new recording, both IDs are generated UUIDs)
      • Multiple files (2 new apps, 2 new recordings, all IDs are generated UUIDs)
      • RRD w/ RBL (new app and recording with predefined IDs)
      • RRD w/o RBL (new app and recording with predefined IDs)
      • RBL (new app with predefined ID)
    • In pre-existing recording:
      • Single file (new app, new recording, both IDs are generated UUIDs)
      • Multiple files (2 new apps, 2 new recordings, all IDs are generated UUIDs)
      • RRD w/ RBL (new app and recording with predefined IDs)
      • RRD w/o RBL (new app and recording with predefined IDs)
      • RBL (new app with predefined ID)
  • Import:
    • In welcome screen:
      • Single file (new app, new recording, both IDs are generated UUIDs)
      • Multiple files (single new app, single new recording, both IDs are generated UUIDs)
      • RRD w/ RBL (new app and recording with predefined IDs)
      • RRD w/o RBL (new app and recording with predefined IDs)
      • RBL (new app with predefined ID)
    • In pre-existing recording:
      • Single file (imports into existing recording, no new app nor recording)
      • Multiple files (imports into existing recording, no new app nor recording)
      • RRD w/ RBL (new app and recording with predefined IDs)
      • RRD w/o RBL (new app and recording with predefined IDs)
      • RBL (updates blueprint for the current app)
• Web:
  • Open:
    • In welcome screen:
      • Single file (new app, new recording, both IDs are generated UUIDs)
      • Multiple files (2 new apps, 2 new recordings, all IDs are generated UUIDs)
      • RRD w/ RBL (new app and recording with predefined IDs)
      • RRD w/o RBL (new app and recording with predefined IDs)
      • RBL (new app with predefined ID)
    • In pre-existing recording:
      • Single file (new app, new recording, both IDs are generated UUIDs)
      • Multiple files (2 new apps, 2 new recordings, all IDs are generated UUIDs)
      • RRD w/ RBL (new app and recording with predefined IDs)
      • RRD w/o RBL (new app and recording with predefined IDs)
      • RBL (new app with predefined ID)
  • Import:
    • In welcome screen:
      • Single file (new app, new recording, both IDs are generated UUIDs)
      • Multiple files (single new app, single new recording, both IDs are generated UUIDs)
      • RRD w/ RBL (new app and recording with predefined IDs)
      • RRD w/o RBL (new app and recording with predefined IDs)
      • RBL (new app with predefined ID)
    • In pre-existing recording:
      • Single file (imports into existing recording, no new app nor recording)
      • Multiple files (imports into existing recording, no new app nor recording)
      • RRD w/ RBL (new app and recording with predefined IDs)
      • RRD w/o RBL (new app and recording with predefined IDs)
      • RBL (updates blueprint for the current app)
• SDK:
  • log_file:
    • Single file (merges nicely into active recording)
    • RRD w/ RBL (new app and recording with predefined IDs)
    • RRD w/o RBL (new app and recording with predefined IDs)
    • RBL (updates blueprint for the current app)

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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 examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• 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!
• If have noted any breaking changes to the log API in CHANGELOG.md and the migration guide

• PR Build Summary
• Recent benchmark results
• Wasm size tracking

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

[teh-cmc]

@rerun-bot full-check

[github-actions]

Started a full build: https://github.com/rerun-io/rerun/actions/runs/11690170174

[emilk]

Well, that was indeed painful and complicated, but I see no obvious better way. 👍