release-24.1: opt: don't apply huge cost for full scans of virtual tables

[blathers-crl]

Backport 1/1 commits from #123780 on behalf of @yuzefovich.

/cc @cockroachdb/release

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This commit fixes - what I believe is - an oversight where we applied the huge cost to the plans with full scans of virtual tables when disallow_full_table_scans variable is set. The intent behind this penalty is to make plans with full scans prohibitively expensive so that other plans (without full scans) would be preferred, and if there is no other plan, then the query would error out. Implementation of this approach was incomplete for virtual tables: namely, we'd apply the cost penalty, but then we would not actually error out the query. Additionally, given that we don't have stats on virtual tables, we would apply the cost penalty to all full scans of virtual tables.

As a result, we would either pick a plan without the full scan (that might actually be worse) or would allow the plan with the full scan to get executed still. We would also favor plans with fewer full scans of virtual tables (which might also be worse than had we not applied the cost penalty). This commit adjusts the code to not apply the cost penalty to full scans of virtual tables.

This change is gated based on the new session variable optimizer_apply_full_scan_penalty_to_virtual_tables which defaults to false on master. We can discuss on the backport PRs whether it should be default to true there to require users to opt in for this PR to have an effect.

Fixes: #122708.

Release note: None

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Release justification: bug fix.

[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.
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  here).
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backport.

[cockroach-teamcity]

This change is 

[DrewKimball]

Reviewed 17 of 17 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @mgartner, @michae2, @rytaft, and @yuzefovich)

[michae2]

Reviewed 17 of 17 files at r1, all commit messages.
Reviewable status: complete! 2 of 0 LGTMs obtained (waiting on @mgartner, @rytaft, and @yuzefovich)