Log emulator's clipboard access to logcat

to help debugging clipboard issues.

Bug: 219611030
Bug: 206758809
Test: boot the emulator with
Test: `-append-userspace-opt androidboot.qemu.log_clipboard_access=1`
Test: use the clipboard, check the logcat for
Test: messages from EmulatorClipboardMonitor
Signed-off-by: Roman Kiryanov <rkir@google.com>
Change-Id: I7fc0a96560f4e9805fd3bc91cb5b40a1fc149141