Guard tooltip delay localStorage read

What does this MR do and why?

Guards the tooltip-delay localStorage read in the global boot path (app/assets/javascripts/main.js) so it no longer throws SecurityError: Failed to read the 'localStorage' property from 'Window' in browsers that deny storage access (e.g. blocked cookies/storage on Chrome Mobile).

Because main.js runs on every page, this unguarded read surfaced across a wide spread of feature_category values in Sentry. The fix:

• Wraps the read with the existing AccessorUtilities.canUseLocalStorage() guard, which safely probes storage access.
• Parses the value via the existing getStorageValue() helper instead of an inline unguarded JSON.parse.
• Falls back to the default tooltip delay of 0 when storage is unavailable, preserving existing behaviour.

The gl-tooltip-delay key is a dev/debug convenience with no other readers/writers, so guarding the read carries no functional risk. User-facing impact of the bug was nil (tooltips would simply use the default delay), but the error created steady Sentry noise.

References

• Resolves https://gitlab.com/gitlab-org/gitlab/-/work_items/631040

Screenshots or screen recordings

No UI change — this only guards a localStorage read. Behaviour is unchanged except that storage-denied browsers no longer throw.

Before	After
N/A	N/A

How to set up and validate locally

1. In Chrome DevTools, block third-party cookies / site data (or run in a context where window.localStorage access is denied).
2. Load any GitLab page.
3. Before: SecurityError is thrown from main.js when reading localStorage.getItem('gl-tooltip-delay').
4. After: no error; tooltips initialize with the default delay of 0.

MR acceptance checklist

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