[Bug]: truncate splits emoji into broken surrogate pairs #27842

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

packages/shared

Steps to reproduce

Call truncate("👍👍👍👍", 3) (or any odd maxLength on emoji-heavy text used for titles / work-log labels).

Expected behavior

Whole emoji only, e.g. "👍👍👍...".

Actual behavior

slice cuts mid-surrogate, producing a lone high surrogate before "...".

Impact

Minor bug or occasional failure

Fix

#27841