Add option to resize GPT when flashing it.

Supports an option to resize GPT and extend the last partition entry to
cover the unused storage space when flashing. This allows devices with
varying disk sizes to use the same GPT for flashing.

Syntax is:

  fastboot flash gpt/<blk_id>/resize

Bug: 374792430

Change-Id: I755390776ca9c01d1fa2c90497a35937d60bdba0