Long empty tooltip is displayed when hovering over UI Builder selector with a long name

Reproduction steps:
1. Create a new project
2. Create > UI Toolkit > UI Document
3. Double-click on newly created UI Document Asset to open UI Builder
4. Click on “+” button in StyleSheets section and select “” option
5. Enter USS File name and save it
6. Enter selector name with 16383 characters or longer in “Add new selector…” field
7. Hover over newly added selector for the tooltip to appear

Actual result: Empty tooltip appears
Expected result: Tooltip displays selector name

Reproducible with:  6000.5.0a3, 6000.5.0b2, 6000.6.0a2
Not reproducible with: 6000.0.72f1, 6000.3.12f1, 6000.4.1f1, 6000.5.0a2

Reproduced on: macOS Tahoe 26.3 (M4), Ubuntu 24.04

Note: Editor freezes for some time after adding the selector