⚡️ [RUMF-902] enable new mutation observer

[BenoitZugmeyer]

Motivation

Enable the mutation observer introduced in #810

Changes

• Remove the experimental flag usages
• Remove now unused related code
• Move the MutationController into mutationObserver

Note

While working on this, I started thinking about a more in-depth cleaning in two ways:

• redesign the 'rrweb-snapshot' logic. I did not forget about this comment, and I think we can drastically simplify the design of the whole file, for example to avoid serializing ignored nodes.

• move modules around. I'd like to:

  • move rrweb-snapshot (serialization logic) and the privacy module closer to the rest of the 'rrweb' codebase
  • rename domain/rrweb to domain/record
  • rename domain/{segment,segmentCollection,deflateWorker} to domain/segmentCollection/*

This will be done later, in separate PRs though.

Testing

Unit, E2E

---

I have gone over the contributing documentation.

[bcaudan]

LGTM 🔥

[vlad-mh]

makes sense to me, thanks for the cleanup Benoit!
the follow up plan seem good as well, I'll be happy to see those PRs

[codecov-commenter]

Codecov Report

Merging #842 (419e894) into main (36683df) will increase coverage by 1.50%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #842      +/-   ##
==========================================
+ Coverage   86.75%   88.25%   +1.50%     
==========================================
  Files          82       81       -1     
  Lines        3918     3670     -248     
  Branches      884      821      -63     
==========================================
- Hits         3399     3239     -160     
+ Misses        519      431      -88     

Impacted Files	Coverage Δ
packages/rum-recorder/src/boot/recorder.ts	100.00% <ø> (ø)
...es/rum-recorder/src/domain/rrweb-snapshot/types.ts	100.00% <ø> (ø)
packages/rum-recorder/src/domain/rrweb/types.ts	100.00% <ø> (ø)
packages/rum-recorder/src/domain/rrweb/utils.ts	83.33% <ø> (+0.35%)	⬆️
...rum-recorder/src/domain/rrweb-snapshot/snapshot.ts	80.91% <100.00%> (+0.58%)	⬆️
.../rum-recorder/src/domain/rrweb/mutationObserver.ts	99.15% <100.00%> (+0.04%)	⬆️
packages/rum-recorder/src/domain/rrweb/observer.ts	76.33% <100.00%> (-0.53%)	⬇️
packages/rum-recorder/src/domain/rrweb/record.ts	63.04% <100.00%> (-0.96%)	⬇️
packages/rum-core/src/transport/batch.ts	74.28% <0.00%> (+11.42%)	⬆️

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