Name flags to be able to edit them with adb

The adb command will be:

```
adb shell setprop persist.wm.debug.desktop_experience.add_dev_option.BASENAME
```

Where `BASENAME` is the last part of the flag (after the last dot), for
example the base name of
`com.android.window.flags.enable_connected_displays_dnd` is
`enable_connected_displays_dnd`.

Test: atest DesktopExperienceFlagsTest
Fix: 408432634
Flag: com.android.window.flags.show_desktop_experience_dev_option
Change-Id: I61352bf14a31e505c0536381711a2e70a63752df