optimize recv_fix_encryption_hierarchy()

[gamanakis]

Motivation and Context

Motivation: #16317
Closes: #16317

Description

recv_fix_encryption_hierarchy() in its present state goes through all
stream filesystems, and for each one traverses the snapshots in order to
find one that exists locally. This happens by calling guid_to_name() for
each snapshot, which iterates through all children of the filesystem.
This results in CPU utilization of 100% for several minutes (for ~1000
filesystems on a Ryzen 4350G) for 1 thread at the end of a raw receive
(-w, regardless whether encrypted or not, dryrun or not).

Fix this by following a different logic: using the top_fs name, call
gather_nvlist() to gather the nvlists for all local filesystems. For
each one filesystem, go through the snapshots to find the corresponding
stream's filesystem (since we know the snapshots guid and can search
with it in stream_avl for the stream's fs). Then go on to fix the
encryption roots and locations as in its present state.

Avoiding guid_to_name() iteratively makes
recv_fix_encryption_hierarchy() significantly faster (from several
minutes to seconds for ~1000 filesystems on a Ryzen 4350G).

How Has This Been Tested?

An existing test was expanded.
Perfomance testing was done locally using the script from #16317

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.