[roll] Roll fuchsia [pkg-cache][pkgfs][fshost] pkg-cache provides all pkgfs directories

All pkgfs directories (including pkgfs/, pkgfs/packages/,
pkgfs/versions/, and pkgfs/system/) are now provided by pkg-cache
instead of pkgfs.

Package directories themselves (including the elements of
pkgfs/versions/ and pkgfs/packages/*/*/ and the /pkg directory mounted
in components' namespaces) are now served by pkg-cache instead of
pkgfs.

The pkgfs directories and package directories themselves are
implemented on top of the Rust VFS library. As a result, they now
enforce hierarchical rights (e.g. opening a file with RIGHT_READABLE
requires that the directory connection over which the
fuchsia.io/Directory.Open FIDL call was made had RIGHT_READABLE) and
perform more validation of the flag, mode, and path
arguments (e.g. paths of the empty string and paths containing ".."
segments are now rejected). See
https://cs.opensource.google/fuchsia/fuchsia/+/main:src/sys/pkg/tests/pkgdir/README.md
for a full listing of the package directory behavior changes.

fshost no longer starts pkgfs (sometimes called pkgsvr).

pkg-cache is now routed an executable handle to blobfs (so it can serve
package directories).

pkg-cache is now a child of bootstrap and is resolved by the
base-resolver.

pkg-cache's other package APIs (fuchsia.pkg/PackageCache.{Open|Get}) now
use the same machinery that powers its pkgfs replacements (instead of
forwarding to pkgfs).

Original-Bug: 99148
Original-Fixed: 88871
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/630466
Original-Revision: 021b6cdc9d9e0bd5f91f5a083fec30e7dfd1791f
GitOrigin-RevId: c696018a852fb8bbe4cfa557b1a22554a9489133
Change-Id: I1c2e69f3ac23e83715d3feaebd9a0165ba3127ba