Let toshikikikuchi@ owns DesktopMode* files

This CL lets toshikikikuchi@ owns DesktopMode* files to approve
desktop-first mode related changes.
The regex includes the following files
- DesktopModeLaunchParamsModifier.java
- DesktopModeHelper.java
- DesktopModeBoundsCalculator.java
- and their test files

Flag: EXEMPT - add owner
Bug: 424287003
Test: m
Change-Id: I19e627ae64f9abe47f33c8566d19354e16204136