MID-10905 Add input variable to existence mappings

[kay1313]

Summary

Fixes MID-10905 by exposing the documented input variable in resource activation existence mappings.

Existence mappings already used the computed projection legality value as the default source named legal. However, the documentation says that the same legality value is available as input. Expressions explicitly referencing input failed with No such property: input.

This change keeps legal as the default source to preserve existing behavior, including <asIs/>, and adds input as an additional source backed by the same legality IDI.

Changes

• Added input as an additional source in ActivationProcessor.evaluateExistenceMapping.
• Kept legal as the default source for backward compatibility.
• Added a regression resource with an existence mapping that checks input == legal and returns input.
• Added test830ExistenceInput covering both:
  • assigned/legal projection creates the account
  • unassigned/illegal projection deletes the account
• Added release note entry.

Manual verification

Verified manually in GUI using a resource existence mapping script that throws debug output.

On the fixed branch, the existence mapping saw:

• assigned case: input=true, legal=true, assigned=true, focusExists=true
• unassigned case: input=false, legal=false, assigned=false, focusExists=true

On current master, the same mapping failed with:

Groovy Evaluation Failed: No such property: input

The master error context contained legal, assigned, and focusExists, but not input.