Revert "[vm/concurrency] Introduce concept of Isolate Groups"

This reverts commit b75057b6876cfa03696309c7a9ca3e2788896f34.

Reason for revert: Caused some failures on app-jit builders

Original change's description:
> [vm/concurrency] Introduce concept of Isolate Groups
> 
> An Isolate Group (IG) is a collection of isolates which were spawned from the
> same source. This allows the VM to:
> 
>   * have a guarantee that all isolates within one IG can safely exchange
>     structured objects (currently we rely on embedder for this
>     guarantee)
> 
>   * hot-reload all isolates together (currently we only reload one
>     isolate, leaving same-source isolates in inconsistent state)
> 
>   * make a shared heap for all isolates from the same IG, which paves
>     the way for faster communication and sharing of immutable objects.
> 
> All isolates within one IG will share the same IsolateGroupSource.
> 
> **Embedder changes**
> 
> This change makes breaking embedder API changes to support this new
> concept of Isolate Groups: The existing isolate lifecycle callbacks
> given to Dart_Initialize will become Isolate Group lifecycle callbacks.
> A new callback `initialize_isolate` callback will be added which can
> initialize a new isolate within an existing IG.
> 
> Existing embedders can be updated by performing the following renames
> 
>   Dart_CreateIsolate -> Dart_CreateIsolateGroup
>   Dart_IsolateCreateCallback -> Dart_IsolateGroupCreateCallback
>   Dart_IsolateCleanupCallback -> Dart_IsolateGroupShutdownCallback
>   Dart_CreateIsolateFromKernel -> Dart_CreateIsolateGroupFromKernel
>   Dart_CurrentIsolateData -> Dart_CurrentIsolateGroupData
>   Dart_IsolateData -> Dart_IsolateGroupData
>   Dart_GetNativeIsolateData -> Dart_GetNativeIsolateGroupData
>   Dart_InitializeParams.create -> Dart_InitializeParams.create_group
>   Dart_InitializeParams.cleanup -> Dart_InitializeParams.shutdown_group
>   Dart_InitializeParams.shutdown -> Dart_InitializeParams.shutdown_isolate
> 
> By default `Isolate.spawn` will cause the creation of a new IG.
> 
> Though an embedder can opt-into supporting multiple isolates within one IG by
> providing a callback to the newly added `Dart_InitializeParams.initialize_isolate`.
> The responsibility of this new callback is to initialize an existing
> isolate (which was setup by re-using source code from the spawning
> isolate - i.e. the one which used `Isolate.spawn`) by setting native
> resolvers, initializing global state, etc.
> 
> Issue https://github.com/dart-lang/sdk/issues/36648
> Issue https://github.com/dart-lang/sdk/issues/36097
> 
> Change-Id: I82437ac017ca33018d45e02f353b0672db155f6a
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/105241
> Commit-Queue: Martin Kustermann <kustermann@google.com>
> Reviewed-by: Ryan Macnak <rmacnak@google.com>
> Reviewed-by: Alexander Aprelev <aam@google.com>

TBR=kustermann@google.com,aam@google.com,rmacnak@google.com

Change-Id: Ibd90992a01d61188f27b445c21532e0c46f996ea
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/107405
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>
27 files changed
tree: 3d2d7be9d6c1668cefef7b3bf95f840fb781dc26
  1. .github/
  2. build/
  3. client/
  4. docs/
  5. pkg/
  6. runtime/
  7. samples/
  8. samples-dev/
  9. sdk/
  10. tests/
  11. third_party/
  12. tools/
  13. utils/
  14. .clang-format
  15. .gitattributes
  16. .gitconfig
  17. .gitignore
  18. .gn
  19. .mailmap
  20. .packages
  21. .vpython
  22. AUTHORS
  23. BUILD.gn
  24. CHANGELOG.md
  25. codereview.settings
  26. CONTRIBUTING.md
  27. DEPS
  28. LICENSE
  29. PATENTS
  30. PRESUBMIT.py
  31. README.dart-sdk
  32. README.md
  33. WATCHLISTS
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