opt: do not build placeholder scans with stable functions

[mgartner]

In v25.4.0 we introduced an optimization for some types of generic query plans which converts parameterized lookup joins into placeholder scans. Prior to this commit the spans of these placeholder scans could contain scalar expressions that were not constants nor placeholders, which execbuilder does not support. This has been fixed by being more strict in the application of this rule.

Fixes #159124

Release note (bug fix): A bug has been fixed which could cause prepared statements to fail with the error message "non-const expression" when they contained filters with stable functions. This bug has been present since 25.4.0.

[cockroach-teamcity]

This change is 

[michae2]

blathers backport release-25.4.2-rc

[mgartner]

TFTR!

bors r+

[craig[bot]]

Build succeeded:

• docker_image_amd64
• acceptance
• lint
• local_roachtest
• examples_orms
• linux_amd64_fips_build
• linux_amd64_build
• check_generated_code
• local_roachtest_fips
• unit_tests

[blathers-crl[bot]]

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

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

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:bulb: Consider backporting to the fork repo instead of the main repo. See instructions for more details.

error creating merge commit from 9a05cd0113f4a74a8a61fde4e336ad29e8768751 to blathers/backport-release-25.4-159201: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 25.4.x failed. See errors above.

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