fix:[M3-10335] - useIsPageScrollable hook is not working correctly for slightly taller pages

[bill-akamai]

Description 📝

This PR fixes the useIsPageScrollable returning false on slightly taller pages by including footer height in the calculation.

Changes 🔄

• Added FOOTER_HEIGHT constant to packages/manager/src/features/Footer.tsx
• Updated useIsPageScrollable hook to include this height in the scrollability calculation

Scope 🚢

Upon production release, changes in this PR will be visible to:

• All customers
• Some customers (e.g. in Beta or Limited Availability)
• No customers / Not applicable

Preview 📷

Before	After
isPageScrollable is false when main content is cut off	isPageScrollable is true at target location

Reproduction steps

Reproduction of this bug is kind of tricky but here's what you can do:

• On line 179 of packages/manager/src/Root.tsx add this log: console.log('isPageScrollable', isPageScrollable);
• Navigate to a Linode's networking page (/linodes/[linode id]/networking)
• Resize your browser's height so that the page content just fits inside your viewport without overflow (you may need to use a larger external monitor for this)
• With the console open, adjust your browser height and observe that isPageScrollable does not return true until a portion of the content is cut off rather than the threshold target from the screenshot above.

Verification steps

• Follow the reproduction steps above and confirm isPageScrollable returns true at the approximate target line location from the screenshot above.

Author Checklists

As an Author, to speed up the review process, I considered 🤔

👀 Doing a self review
❔ Our contribution guidelines
🤏 Splitting feature into small PRs
➕ Adding a changeset
🧪 Providing/improving test coverage
🔐 Removing all sensitive information from the code and PR description
🚩 Using a feature flag to protect the release
👣 Providing comprehensive reproduction steps
📑 Providing or updating our documentation
🕛 Scheduling a pair reviewing session
📱 Providing mobile support
♿ Providing accessibility support

• I have read and considered all applicable items listed above.

As an Author, before moving this PR from Draft to Open, I confirmed ✅

• All tests and CI checks are passing
• TypeScript compilation succeeded without errors
• Code passes all linting rules

[github-actions]

This PR is stale because it has been open 15 days with no activity. Please attend to this PR or it will be closed in 5 days

[linode-gh-bot]

Cloud Manager UI test results

🎉 738 passing tests on test run #5 ↗︎

❌ Failing	✅ Passing	↪️ Skipped	🕐 Duration
0 Failing	738 Passing	6 Skipped	53m 21s

[dwiley-akamai]

I don't have a large external monitor, but I tested by zooming out to 75% on the page, and was able to confirm isPageScrollable doesn't return as true until I shrink the vertical size smaller than the approximate line shown.

[coliu-akamai]

same with Dajahi, I don't have a super large monitor but tested with zooming out on the page - things are looking good

thanks @bill-akamai!