[roll] Roll fuchsia [Component Manager] Add Rust Bootfs

Initial commit for adding a Rust version of the Bootfs filesystem in
component manager, with the overall goal of removing bootsvc from the
bootstrap process.

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This change is functionally gated by the flag "--host_bootfs".
When set, the bootsvc C++ bootfs service is uninstalled from the
namespace and it is replaced by the Rust bootfs service. This happens
before component manager uses anything in '/boot', so it remains a good
proof of concept.

While Fuchsia can boot with this new bootfs service (tested by removing
the handle passed to component manager), please note two things before
enabling this flag:
1) There's currently a problem with the Rust VFS which is setting
invalid INODES, meaning things like "ls -R" will think there's a loop.
2) Since the C++ bootfs is still being created we'll be wasting memory.

Next steps are:
1) Fix the invalid INODE issue.
2) Stop creating the C++ bootfs in bootsvc when this flag is set.
3) Port the C++ integration test over to a Rust system test.

Original-Bug: 44784

Testing:
This WIP implementation has only currently been manually tested by
verifying that the created /boot directory served the same files with
the same permissions.

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/619308
Original-Revision: 48da0ac29ba4e750e8374ddc12b65135a717910e
GitOrigin-RevId: 54772727fbcdea25391e2e6cc8efdef1e2b21f41
Change-Id: I92fb9f593b33bd68ea54737e8ab809796dfdca77