refactor(docs-infra): extract magic 27 in navigation-list tooltip thr…

[erkamyaman]

The matTooltip on navigation list items was disabled when the label was shorter than the literal 27, repeated across four bindings in the template. Lift the value to a protected readonly field so the threshold has a name and lives in one place.

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?

The matTooltipDisabled binding on each navigation list item compares the label length against a literal 27, repeated four times across the template.

What is the new behavior?

The threshold is extracted to a protected readonly labelTruncationThreshold = 27 field on NavigationList and the four template bindings reference it by name. No functional change.

Does this PR introduce a breaking change?

• Yes
• No