fix: close mobile nav on blur of nav list

[SatyamSetia]

Describe your changes

This PR contains 2 changes as follows -

1. Solves the issue #379
2. Minor refactoring - rename state variables in Layout.tsx and related child components and stories (name changed from showNavMobile to isNavMobileOpen)

Link to issue

Closes #379

Checklist before requesting a review

• [x] I have performed a self-review of my code.
• [x] Followed the repository's Contributing Guidelines.
• [x] I ran the app and tested it locally to verify that it works as expected.
• [x] I have checked my code with an automatic accessibility tool such as Axe Dev Tools or Wave and it shows no errors.

Additional Information (Optional)

Any additional information that you want to give us.

[SatyamSetia]

Hey, @EmmaDawsonDev Requesting your review on this PR whenever you get time.