Use unique_ptr for CommandEntry

Currently, there is some unusual behaviour happening for CommandEntries.
The entry is created and pushed onto a queue, but a pointer to the entry
is returned in order to modify the entry after it has been created.

Instead, fully construct the entry before enqueueing it. Also, switch to
using unique_ptr in order to simplify memory management of queue
entries.

Bug: 70668286
Test: SANITIZE_TARGET=hwaddress atest libinput_tests inputflinger_tests
Change-Id: Ie8ee9b732cdcd8f9a391f8315346fe4720d68e58