server: make SpanStats authoritative

[zachlite]

This commit guarantees that SpanStats uses up-to-date range
descriptors on all nodes. The dependency on DistSender is removed
and is replaced with a dependency on rangedesc.Scanner.

rangedesc.Scanner is used to:

1. Locate nodes that house replicas of a span to avoid cluster-wide fan-outs.
2. Find Range Descriptors that touch a span, to build a SpanStatsResponse.

This commit also fixes #103809, where a SpanStatsResponse incorrectly returned
the replica_count for a span, instead of the range_count.

Epic: https://cockroachlabs.atlassian.net/browse/CRDB-24928
Issue: #103957
Release note (bug fix): SpanStats is no longer subject to stale
information, and should be considered authoritative.

[cockroach-teamcity]

This change is 

[knz]

Great work. Thanks for this change. Don't forget to update the test expectation in TestAdminAPITableStats.

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @zachlite)

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-- commits line 8 at r1:
tip: add a blank line after the colon and in-between the two list items to fix the markdown formatting. (You can also upgrade the PR description after that)

[arulajmani]

Reviewed 1 of 5 files at r1, 3 of 5 files at r2, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @knz and @zachlite)

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-- commits line 6 at r2:
To confirm, this only runs on the system tenant, right?

If not, we might need to use a rangedesc.Iterator instead, much like crdb_internal.ranges_no_leases does.

[arulajmani]

Didn't mean to publish just yet. Change looks good, just a question in-line.

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @knz and @zachlite)

[zachlite]

Yep, span stats are fulfilled by the system tenant (KV nodes). Other tenant requests for span stats are forwarded through tenantConnect.

TFTR

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @knz)

[zachlite]

bors r+

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
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You might need to create your backport manually using the backport tool.

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error setting reviewers, but backport branch blathers/backport-release-23.1-104423 is ready: POST https://api.github.com/repos/cockroachdb/cockroach/pulls/105000/requested_reviewers: 422 Reviews may only be requested from collaborators. One or more of the teams you specified is not a collaborator of the cockroachdb/cockroach repository. []

Backport to branch 23.1.x failed. See errors above.

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