Implement restart

[roblourens]

Towards #7670

Also includes some refactoring so that this flow reads more nicely.
I had to

• Flip around the flow of starting a cell debug session- previously it did init work in the command, starting a debug session, instantiating the DA then passing the session object back to the command handler. Now the command only kicks off a debug session, and all the interesting work happens inside the debug adapter factory, which is more straightforward
• Modify the initialize request to add the capability flag that the DA will implement the "restart" request
• Intercept the restart request, and start a new debug session. The reason we have to implement the restart request is because the index of the notebook cell may have changed since the original request, and we will start a launch config using the new index.

Remaining: This is not hooked up for IW debugging yet

[IanMatthewHuff]

Awesome. Looks great.

[codecov-commenter]

Codecov Report

Merging #11668 (fbc6769) into main (543900b) will decrease coverage by 17%.
The diff coverage is 35%.

❗ Current head fbc6769 differs from pull request most recent head 705f8b6. Consider uploading reports for the commit 705f8b6 to get more accurate results

@@           Coverage Diff            @@
##            main   #11668     +/-   ##
========================================
- Coverage     59%      41%    -18%     
========================================
  Files        483      486      +3     
  Lines      34509    34480     -29     
  Branches    5609     5592     -17     
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- Hits       20401    14359   -6042     
- Misses     12128    18908   +6780     
+ Partials    1980     1213    -767     

Impacted Files	Coverage Δ
src/notebooks/debugger/debugger.ts	20% <0%> (+3%)	⬆️
src/notebooks/debugger/kernelDebugAdapterBase.ts	6% <0%> (-1%)	⬇️
src/notebooks/debugger/debuggingManager.ts	31% <11%> (+10%)	⬆️
src/notebooks/debugger/debuggingManagerBase.ts	24% <17%> (-12%)	⬇️
...otebooks/debugger/controllers/restartController.ts	21% <21%> (ø)
...ive-window/debugger/jupyter/debugCellController.ts	22% <25%> (ø)
...active-window/debugger/jupyter/debuggingManager.ts	33% <26%> (+2%)	⬆️
src/notebooks/debugger/commandRegistry.ts	37% <37%> (ø)
...rc/interactive-window/debugger/jupyter/debugger.ts	42% <42%> (ø)
src/notebooks/debugger/helper.ts	19% <42%> (+<1%)	⬆️
... and 274 more