Enable debugger on kernel change

[karlaspuldaro]

Fixes #2902 : Changing kernels disables debugging
With this fix, changing the kernel selection to any kernel that supports debugging enables the debug button accordingly.

What changes were proposed in this pull request?

On kernel change, the kernel was shutdown and restarted, although the debugger service and handlers were not updated for some reason.
A simpler solution was to use the changeKernel method instead of shutdown then startKernel.

Other enhancements:

• Reset run button state after interrupting kernel
• Better handle default kernel selection (not to assume there is a language match with the name property)

How was this pull request tested?

• Added unit tests for default kernel selection + debugging support

Developer's Certificate of Origin 1.1

   By making a contribution to this project, I certify that:

   (a) The contribution was created in whole or in part by me and I
       have the right to submit it under the Apache License 2.0; or

   (b) The contribution is based upon previous work that, to the best
       of my knowledge, is covered under an appropriate open source
       license and I have the right under that license to submit that
       work with modifications, whether created in whole or in part
       by me, under the same open source license (unless I am
       permitted to submit under a different license), as indicated
       in the file; or

   (c) The contribution was provided directly to me by some other
       person who certified (a), (b) or (c) and I have not modified
       it.

   (d) I understand and agree that this project and the contribution
       are public and that a record of the contribution (including all
       personal information I submit with it, including my sign-off) is
       maintained indefinitely and may be redistributed consistent with
       this project or the open source license(s) involved.

[elyra-bot]

Thanks for making a pull request to Elyra!

To try out this branch on binder, follow this link:

[karlaspuldaro]

@lresende this is ready for review :)

[akchinSTC]

@karlaspuldaro - if have kernelspec debugger set to false with

 "display_name": "Python 3 - fakecopy",
 "language": "python",
 "metadata": {
  "debugger": false
 }

should i still be seeing the debugger icon and the ability to activate it?

[karlaspuldaro]

@akchinSTC Thanks for checking this case, that should disable the button, we might need to update some frontend handlers still. Marking this back to WIP

[marthacryan]

Code LGTM but I haven't tested locally yet

[marthacryan]

Just tried it locally and it's working as expected w/ the xeus kernels and built-in kernel.

[akchinSTC]

ok for this to go in as is with follow up pr on the issue I mentioned

[karlaspuldaro]

Follow up issue #2916