fix(material/tooltip): tooltip inside sidenav hides after text update

[yogeshwaran-c]

Summary

• Fixes tooltip inside mat-sidenav hiding when its text content is updated dynamically
• When the tooltip overflows the sidenav (a scrollable ancestor) and its message is updated, updatePosition() triggers the overlay clip check which incorrectly detects the tooltip as clipped and hides it
• Added _isRepositioningForMessage flag to skip the clip check during message-driven repositioning

Root Cause

1. mat-sidenav content extends CdkScrollable, making it a registered scrollable ancestor
2. Updating tooltip message triggers _updateTooltipMessage() → updatePosition() → positionChanges emission
3. The positionChanges subscriber checks isOverlayClipped against scrollable ancestors
4. Since the tooltip overlay (in the global overlay container) extends beyond the sidenav bounds, it's detected as "clipped" and hidden

Test plan

• Added unit test verifying tooltip stays visible when message is updated inside a scrollable container
• CI validates existing tooltip scroll-hide tests still pass
• Manual verification with reproduction from issue

Fixes #27782

🤖 Generated with Claude Code

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[crisbeto]

This is pure hallucinated slop. Please stop pointing your Claude instance at random issues and relying on us to verify if the code it produced actually makes sense.