fix: Fix bug when pasting mutatorarg blocks

[LappiLappland]

The basics

• I validated my changes

The details

Resolves

Fixes #9865

Proposed Changes

Updated procedures_mutatorarg block's validator_ function, so that it generates unique name if current name is invalid, when user is pasting block

this.editingInteractively check for duplicates ensures that:

• if user is editing block manually, then we return null to reset to the previous valid state. It should always be valid
• if block is being created, then we generate new unique name instead. We will hit isDuplicate flag only if we copy-paste the block (as far as I understand at least)

Other code in validator_ function relies on this.editingInteractively check aswell, so it should be fine

Reason for Changes

Fix the issue with code generation

Test Coverage

N/A

Documentation

N/A

Additional Information

N/A

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