create new modeler instance always, but only call getModeler once in useBpmnEditor hook

[standeren]

Description

• Remove singleton modeler instance usage to avoid mismatch in container property and canvasRef when switching tabs in Studio
• Make sure only fetching modeler instance once from useBpmnEditor hook to avoid attaching multiple instances in the same canvas
• Get the corresponding layoutSetId connected to the task when deleting a task with the deleteLayoutSet endpoint

This PR fixes an issue with getting an empty canvas in process-editor when moving between tabs

Related Issue(s)

• #{issue number}

Verification

• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)

[codecov]

Codecov Report

Attention: Patch coverage is 93.75000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 90.17%. Comparing base (43a6c92) to head (02d2f15).

Files	Patch %	Lines
...packages/process-editor/src/hooks/useBpmnEditor.ts	92.85%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #12685   +/-   ##
=======================================
  Coverage   90.17%   90.17%           
=======================================
  Files        1296     1296           
  Lines       18557    18557           
  Branches     2261     2261           
=======================================
  Hits        16733    16733           
  Misses       1564     1564           
  Partials      260      260           

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[nkylstad]

Nice job! I tested this locally as well, with adding and removing some tasks and navigating back and forth. Seems to work as expected!