Remove Mac Catalyst version detection workaround

[jfversluis]

Description of Change

Removes a workaround that was needed earlier to detect the proper Mac Catalyst version number. A fix has been merged into .NET Runtime so we should be good to remove the workaround on our end.

[Copilot]

Pull Request Overview

This PR removes a legacy workaround used for detecting Mac Catalyst version 18 now that a fix has been merged into .NET Runtime. Key changes include:

• Updating version checks in TabbedViewExtensions.cs to use OperatingSystem.IsMacCatalystVersionAtLeast().
• Removing the obsolete OperatingSystemMacCatalyst18Workaround.cs file.
• Updating conditional logic in ShellPageRendererTracker.cs and ShellItemRenderer.cs to reference the updated OS detection methods.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/Core/src/Platform/iOS/TabbedViewExtensions.cs	Updated version check for Mac Catalyst detection.
src/Core/src/OperatingSystemMacCatalyst18Workaround.cs	Removed outdated workaround file.
src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellPageRendererTracker.cs	Updated combined OS version check for tab bar visibility.
src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellItemRenderer.cs	Updated conditional version check for managing tab bar.

Comments suppressed due to low confidence (2)

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellPageRendererTracker.cs:144

• Ensure that there are corresponding test cases in TestCases.HostApp and TestCases.Shared.Tests covering scenarios both when the OS version is below and above 18 to validate the updated conditional behavior.

if (!(OperatingSystem.IsMacCatalystVersionAtLeast(18) || OperatingSystem.IsIOSVersionAtLeast(18)))

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellItemRenderer.cs:441

• Verify that automated tests in both TestCases.HostApp and TestCases.Shared.Tests adequately cover the tab bar state when running on systems with OS versions both under and over 18.

if (OperatingSystem.IsMacCatalystVersionAtLeast(18) || OperatingSystem.IsIOSVersionAtLeast(18))