Support "fastboot fetch"

Adds support for the "fastboot fetch" command that fetches partitions
from the device. Introduces a semantic that supports specifying any sub
range of a GPT partition or raw block device as a "partition" in
Fastboot commands.

Bug: 331257795
Change-Id: I06df9fbb3c63e0d941af808be1fb747084b9f6b8
9 files changed
tree: 54baa267e7f7cd36c27d9b4188eaa349501a0fe3
  1. gbl/
  2. libxbc/
  3. vts/
  4. .gitignore
  5. BUILD
  6. OWNERS