What

Not much else has changed yet except some doc massaging. First step towards solving

• C++ universal "maybeowned" adapting container used everywhere instead of std::vector #3794

rerun::Collection will evolve from here on and be the corner piece of our zero copy & component adaptability strategy (just like ComponentBatch is already!)

This was originally opened on the wrong branch by accident:

• [C++] Rename rerun::ComponentBatch to rerun::Collection (and related constructs) #4225

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 demo.rerun.io (if applicable)
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG

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