fastboot: add optimize-factory-image command

optimize-factory-image command captures commands that fastboot issues during flashing of the update
zip (which is nested in factory image zip) to the script.txt file. Partition images and script.txt
are copied to the output optimized factory image zip. flash-all.sh commands are parsed manually.

Optimized factory image zip is intended to be used by the fastboot.js-based web installer.

Main advantages of using optimized factory images instead of standard images in fastboot.js:
- code for creating optimized super partition image on the fly is reused, which removes the need
to use fastbootd during flashing. fastbootd currently requires manual driver installation on Windows.
- lowering of install-time storage and memory requirements
- simplification of fastboot.js code
- consistency between fastboot and fastboot.js flashing sequence