On mobile, focusing a long nav item shows a matTooltip that escapes the drawer, ignores inner scroll, and blocks scrolling while open. Suppress it on mobile using the existing isMobile helper.

PR Checklist

• The commit message follows our guidelines: https://github.com/angular/angular/blob/main/contributing-docs/commit-message-guidelines.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.dev application / infrastructure changes
• Other... Please describe:

What is the current behavior?

On mobile, focusing a long nav-list item shows a matTooltip that escapes
the drawer onto the page behind it, doesn't track scroll within the drawer,
and blocks scrolling while open.

What is the new behavior?

Tooltip is suppressed on mobile by extending matTooltipDisabled with the
isMobile helper from @angular/docs. Desktop behavior unchanged.

Does this PR introduce a breaking change?

• Yes
• No