Rename PersistentCollection methods to participial forms and deprecate originals

[DmitryNekrasov]

This issue implements a methodological refinement to the PersistentCollection interface to enhance API clarity and align with Kotlin standard library conventions.

Problem

The current PersistentCollection interface uses imperative verb forms (add, remove, clear) that mirror MutableCollection's API, creating semantic ambiguity. While MutableCollection methods perform in-place mutations, PersistentCollection methods return new instances. This behavioral difference is not surfaced at the API level, requiring developers to rely on documentation rather than self-documenting code.

Solution

Apply Kotlin's established naming pattern (like sort() vs sorted()) to distinguish mutating from non-mutating operations. The participial "-ing" suffix immediately communicates that operations produce new instances rather than altering existing state.

Implementation

Introduce new methods with participial naming and deprecate existing imperative verb methods with migration guidance.

PersistentCollection: add → adding, addAll → addingAll, remove → removing, removeAll → removingAll, retainAll → retainingAll, clear → cleared

PersistentList: add(index) → adding(index), addAll(index) → addingAll(index), set(index) → replacingAt(index), removeAt → removingAt

PersistentMap: put → putting, putAll → puttingAll, remove(key) → removing(key), remove(key, value) → removing(key, value), clear → cleared