fix: Android: Splash screen always showing behind other screens

[NicolasMassart]

Description

Cause of the issue

The splash screen has been reworked recently for performances and replaced by an Android window background. But this is visible quickly between screen changes as nav stack has been reorganised.

Fix

• remove the transparent background on MainFlow stack navigator to prevent the window background to be visible behind it

Related issues

Fixes #11697

Manual testing steps

Feature: Navigate between screens without splash screen visible
  Scenario: go to token detail screen
    Given wallet is ready
    And some tokens are available in the list (load from a test address)
    When user touches the token title or icon
    Then detail screen opens
    And no splash screen fox is visible even very quicly.

Note

The issue was on Android but do not hesitate to also test iOS to make sure nothing is broken.

Screenshots/Recordings

Before

See recording in #11697

After

android.webm

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.

[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.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

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

See analysis details on SonarCloud

[github-actions]

Bitrise

✅✅✅ pr_smoke_e2e_pipeline passed on Bitrise! ✅✅✅

Commit hash: 2e7f7e4
Build link: https://app.bitrise.io/app/be69d4368ee7e86d/pipelines/9d5a0067-9ed4-46be-aa6b-4b65d84eee27

Note

• You can kick off another pr_smoke_e2e_pipeline on Bitrise by removing and re-applying the Run Smoke E2E label on the pull request

[salimtb]

LGTM ✅

[chrisleewilcox]

LGTM