fix: Fix error that occurs when dragging a type into an object

[TomasEng]

Description

This pull request fixes an error that occurs when dragging a type into an object in our data modelling tool. This happened because the useAddRreference hook referenced the target parent with uniquePointer instead of schemaPointer. This pull request corrects that, in additon to add measures to prevent it from happening again. Here is a list of the changes:

• Corrected the test data for useAddReference
• Fixed the useAddReference hook
• Made the getUniquePointer and removeUniquePointerPrefix methods on the SchemaModel class static, since they don't depend on this
• Added an end-to-end test for this scenario and improved some Playwright selectors

How to reproduce the error in production

1. Open a data model in studio
2. Create a type and an object
3. Drag the type into the object
4. Observe that no reference to the type is added and that an error message appears in the console

Spiller.inn.2024-10-10.133616.mp4

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

All modified and coverable lines are covered by tests ✅

Project coverage is 94.57%. Comparing base (eeaeece) to head (f49b0ca).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #13762   +/-   ##
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  Coverage   94.57%   94.57%           
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  Files        1623     1623           
  Lines       21797    21800    +3     
  Branches     2570     2570           
=======================================
+ Hits        20615    20618    +3     
  Misses        939      939           
  Partials      243      243           

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[Konrad-Simso]

Nice work 💯

[ErlingHauan]

Fungerer som det skal i test. Bra fiks!