refactor: rename initModularizedControllers to initMessengerClients and update result properties

[cryptodev-2s]

Description

Rename initModularizedControllers to initMessengerClients, drop existingControllersByName, rename controllerInitFunctions to initFunctions, and update return type to messengerClientsByName. Update all consumers in Engine.ts, utils.test.ts, and test utility functions.

80 files changed. PR 3 of 4 — depends on PR 2 (#28641).

• PR 1: Core type renames (Controller → MessengerClient, etc.) (refactor: rename Controller types to MessengerClient types #28610)
• PR 2: CONTROLLER_MESSENGERS → MESSENGER_FACTORIES (refactor: rename CONTROLLER_MESSENGERS to MESSENGER_FACTORIES #28641)
• PR 3 (this): initModularizedControllers → initMessengerClients + utils/Engine.ts renames
• PR 4: Property renames (controller → messengerClient, getController → getMessengerClient) in all init files + tests

Relates to WPC-916.

Changelog

CHANGELOG entry: null

Related issues

Fixes: https://consensyssoftware.atlassian.net/browse/WPC-916

Manual testing steps

Feature: Messenger client init system

  Scenario: App builds and runs normally
    Given the app is built from this branch

    When user opens the app
    Then the app behaves identically to main (no runtime behavior change)

Screenshots/Recordings

N/A — no UI changes.

Before

N/A

After

N/A

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Mobile Coding Standards.
• I've completed the PR template to the best of my ability
• I've included tests if applicable
• I've documented my code using JSDoc format if applicable
• I've applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

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Note

Medium Risk
Touches Engine startup wiring by renaming and reshaping the controller/messenger-client initialization helper; behavior should be equivalent but regressions could prevent controllers from being initialized or retrieved in the correct order.

Overview
Renames the modular engine initialization helper from initModularizedControllers to initMessengerClients, updating its API (controllerInitFunctions → initFunctions) and return shape (controllersByName → messengerClientsByName).

Updates Engine.ts to use the new helper/return value for wiring controller instances into the Engine context, and adjusts the helper to drop support for pre-seeded existingControllersByName in favor of a single progressively-built map.

Renames the associated test utilities (buildControllerInitRequestMock/createMockControllerInitFunction) and updates a large set of controller init tests to use the new mock builder and updated helper/error messages.

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✅ E2E Fixture Validation — Schema is up to date
11 value mismatches detected (expected — fixture represents an existing user).
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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud