release-23.2: cli/doctor, doctor: use right jobs table, skip dropped descs

[annrpom]

Backport 2/2 commits from #123298.

/cc @cockroachdb/release

Release justification: non-production change to debugging tool

---

cli/doctor: doctor should read from the right jobs table

In #97762, we started writing a job's payload (and progress)
information to the system.jobs_info table. As a result, we
had to change the parts of our code that relied on the system.jobs
table to use crdb_internal.system_jobs instead (since that table
would inaccurately report that some payloads were NULL).
This change did not occur for the in-memory representation of the jobs
table created by debug doctor -- which can result in missing job
false-positives. This patch updates debug doctor's representation of
the jobs table by referring to crdb_internal.system_jobs instead.

Epic: none
Fixes: #122675

Release note: None

---

doctor: skip validation for dropped descriptors

In some cases, dropped descriptors appear in our system.descriptors
table with dangling job mutations without an associated job.
This patch teaches debug doctor examine to skip validation
on such dropped descriptors.

Epic: none

Fixes: #123477
Fixes: #122956

Release note: none

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Backports should only be created for serious
  issues or test-only changes.
• Backports should not break backwards-compatibility.
• Backports should change as little code as possible.
• Backports should not change on-disk formats or node communication protocols.
• Backports should not add new functionality (except as defined
  here).
• Backports must not add, edit, or otherwise modify cluster versions; or add version gates.
• All backports must be reviewed by the owning areas TL and one additional
  TL. For more information as to how that review should be conducted, please consult the backport
  policy.

If your backport adds new functionality, please ensure that the following additional criteria are satisfied:

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters. State changes must be further protected such that nodes running old binaries will not be negatively impacted by the new state (with a mixed version test added).
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.
• Your backport must be accompanied by a post to the appropriate Slack
  channel (#db-backports-point-releases or #db-backports-XX-X-release) for awareness and discussion.

Also, please add a brief release justification to the body of your PR to justify this
backport.

[cockroach-teamcity]

This change is 

[rafiss]

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @annrpom, @nameisbhaskar, and @vidit-bhat)

---

pkg/sql/doctor/doctor_test.go line 200 at r2 (raw file):

			},
			valid:    true,
			expected: "Examining 1 descriptors and 0 namespace entries...\n",

nit: just noticed this. why are we removing the expected error check?

---

pkg/sql/doctor/doctor_test.go line 419 at r2 (raw file):

			},
			valid:    true,
			expected: "Examining 2 descriptors and 1 namespace entries...\n",

nit: just noticed this. why are we removing the expected error check?