test(Tasks): add test suite for multi-select-utils

[adiprathapa]

Added 16 tests for getFilteredItems and shouldShowCreateOption in multi-select-utils.ts. To test run npx jest --testPathPattern="multi-select-utils" --verbose

Ref #300

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[adiprathapa]

Wrote tests for getFilteredItems and shouldShowCreateOption, test names are self explanatory as to what they cover.