[a11y] Improve the accesbility of the AdvancedDrawer widget

[luke-genvis]

Description of the Issue

Currently, the AdvancedDrawer widget has several accessibility issues that are difficult to resolve outside the package:

• Nav drawer items remain accessible via screen readers and physical keyboards when the drawer is closed
  • Failure of WCAG 2.4.3: Focus Order
• Content behind an open drawer can still be interacted with using screen readers or keyboards
  • Failure of WCAG 2.4.11: Focus Not Obscured (Minimum)
• The drawer close button lacks a semantic label, making its purpose unclear for screen reader users
  • Failure of WCAG 4.1.2: Name, Role, Value

Reference: Flutter Accessibility Documentation

Changes

• Added drawerCloseSemanticLabel field to provide a semantic label for the close button
• Implemented ExcludeFocus and ExcludeSemantics widgets in appropriate places
• Made minor optimizations, such as using Visibility widget where possible

Visual Demonstration

Screen Reader Navigation

Before	After
screen-20250310-224548.mp4	screen-20250310-224308.mp4

External Bluetooth Keyboard Navigation

Note

The focus_debugger package was used to visualize the focused element.

It should be noted debugger has a issue where the box occupies the entire screen when focus is lost. In the video, this just indicates that the focus node element no longer exists in the focus tree (Due to the addition of ExcludeFocus)

Before	After
screen-20250310-224645.mp4	screen-20250310-224745.mp4