refactor: name the shielded methods after the transparent side they touch

[LexxXell]

Problem

SHIELD_TO_POOL says the same thing twice: shielding is moving funds into the shielded pool. The half that carries information is missing - where the funds come from, which is one of the wallet's own Platform addresses and is even a parameter of the call.

It also breaks the symmetry of its neighbours. UNSHIELD_TO_ADDRESS and WITHDRAW_SHIELDED_TO_CORE are named after the transparent side of the operation, which for shielding is the source. And UNSHIELD_TO_ADDRESS does not say which address, although leaving the pool for a Core address is a different method entirely.

The SDK itself calls the transition plainly shield, without repeating the pool.

Changes

• SHIELD_TO_POOL → SHIELD_FROM_PLATFORM_ADDRESS, handler ShieldFromPlatformAddressHandler, payload and response renamed to match, file renamed.
• UNSHIELD_TO_ADDRESS → UNSHIELD_TO_PLATFORM_ADDRESS, same treatment.
• Client methods are shieldFromPlatformAddress and unshieldToPlatformAddress. The old names stay as @deprecated one-line aliases that delegate to them, so every existing caller keeps working and the UI needs no change in this PR.

All the shielded methods now read by one rule: they name the transparent side, and the naming lines up with the new funding methods (REGISTER_IDENTITY_FROM_PLATFORM_ADDRESS, TOP_UP_IDENTITY_FROM_PLATFORM_ADDRESS).

Backend only - no UI changes.

Testing

• tsc --noEmit, ts-standard, npm run build
• jest: 42 suites, 361/361. The handler spec moved with its file and now covers ShieldFromPlatformAddressHandler.
• grep finds no remaining reference to the old messaging methods or handler names outside the deprecated client aliases.

[LexxXell]

Переношу переименование в #170: замечание пришло по нему, и он уже правит те же файлы. Отдельный PR не нужен.