chore: centralize redesigned confirmation decision logic

[cryptotavares]

Description

This PR centralizes the redesigned confirmation decision logic to improve code organization and reduce duplication across the codebase. Currently, redesign confirmation decision logic is scattered across multiple files, making it harder to maintain and more prone to inconsistencies.

Motivation

The existing implementation has several issues:

1. Duplicate logic for handling confirmation decisions across different transaction types
2. Prevent inconsistent handling of redesigned confirmation flows

Key changes:

• Move supported redesigned confirmation decision logic to the shared dir (to be used both in the ui and app bundles)
• Updated signature metrics tracking to support developer mode enabled

Types of changes:

• Code style update (changes that do not affect the meaning of the code)

Related issues

Fixes:

Manual testing steps

1. Ensure that when either the experimental confirmations redesign toggle, developer option confirmations redesign toggle or the env ENABLE_CONFIRMATIONS_REDESIGN is enabled the we are presenting the new redesign confirmations.

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension 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.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[sentry-io]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: app/scripts/lib/createRPCMethodTrackingMiddleware.js

Function	Unhandled Issue
finalizeSignatureFragment	Error: Event fragment with id signature-911707255 does not exist. /sc... Event Count: 1 Affected Users: 0

📄 File: app/scripts/lib/transaction/metrics.ts (Click to Expand)

Function	Unhandled Issue
buildEventFragmentProperties	TypeError: null has no properties /background.html Event Count: 20 Affected Users: 0
buildEventFragmentProperties	SyntaxError: Invalid or unexpected token /scripts... Event Count: 7 Affected Users: 0
buildEventFragmentProperties	TypeError: Cannot destructure property 'name' of '(intermediate value)' as it is null. ... Event Count: 5 Affected Users: 0
buildEventFragmentProperties	TypeError: e.ￇ槌ￔ榫ￅ槝iceModel is not a function /sc... Event Count: 4 Affected Users: 0

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