Add task limit flags to the Dev Options.

Update the call sites for enableDesktopWindowingTaskLimit and add the
new-style flag in dev options.

Also correct a few comments in the DesktopTasksLimiter class.

Fix: 356069386
Test: Build and check that enabled dev option enable task limit
Flag: EXEMPT (updating how the flags are called)
Change-Id: Id7633120b5da16b9d5be26c99fbd3c54599d0928