Fix #104958

#104772

Fix #105195

open overwrite should re-use existing editor even when the editor is optional, https://github.com/microsoft/vscode/issues/99496

borrow notebook editors from a notebook widget service. let the service manage editor move and deal with group changes

nuke NotebookEditorModelManager, add ref-counting notebook resolver service, don't cache or re-create notebook editor inputs, cache notebook widgets by "tab id" (uri and group), extract move spy'ing into separate open override handler

* editor override - remove id property and rely on options.override instead

* custom editors - code cleanup

* :lipsick:

* Support view type for creating new untitled file.
Co-authored-by: NBenjamin Pasero <benjpas@microsoft.com>

make sure to resolve notebook during cell content provide, https://github.com/microsoft/vscode/issues/99148

share undo stack between text models in a notebook. the undo stack is not shared with notebook itself yet due to #98750.