[blobfs] Avoid double-counting duplicated blobs

During the image generation process, space is pre-calculated for the
underlying image based on the manifest of blobs which have been
provided. Since blobs are content-addressable and naturally duplicated
by blobfs, it is possible that multiple blobs with the same contents
will consume less space than they would individually.

This patch modifies the host-side tools to pre-generate the merkle
trees (once), find the unique set of blobs within them, and only
allocate / attempt to add blobs after they have been deduplicated.

This shrinks the generated "fvm.blk" image from 736 MB -> 394 MB
for the Astro build.

Test: host FVM tests, manually building
ZX-2141 #comment In Progress
US-441 #comment In Progress

Change-Id: I1ccdab91e74691e607f27419582dadbe7ced97e9

[minfs] Support for generating depfile

Similarly to change that has been made to blobfs, we add support
for generating depfile to the minfs host tool.

Test: manual
Change-Id: I337b0ef0cd70f7ccfe894f8d020ed5d1a97235a4

[blobfs] [minfs] [host] Combine common functionality between tools

De-dupe code between the minfs and blobfs host side tools as much as
possible. Additionally, add minfs support for adding manifests on create.

ZX-2033 #done

Change-Id: I0ece73d37927e6589ccd7d1ce235fc484668a221

[minfs] Clean up option parsing

ZX-1770 #done
ZX-1724 #done

Change-Id: Ic1afe498f2a0dab31965f09c32273254a070236c

[minfs] Correctly handle absolute paths from manifest

US-436 #done

Change-Id: Ifa10a82f3414225304b7babe8b77da2711d2e954

[minfs][host] Ignore existing directories in cp.

This change makes it so that existing directories are ignored
when a recursive copy is attempted. Before, if the directory tree
existed, the MinFS host tool would error.

Change-Id: I125ff0869c3dd53f3c5aa09fdb1ff65a2bde1457

[minfs] Convert minfs.h into private interface

Change-Id: I3a0fe542871172b591a0f178eb1d855f12742558

[minfs][blobstore][fvm] Relocate host-side tools to /host

Change-Id: I21e3f17a7dd926dc5038af85edc0e2e016d220bd