sql: add framework for testing only descriptor validation

[arulajmani]

This patch adds a new field on the ExecutorTestingKnobs called
TestingDescriptorValidation. This creates the structure to perform
certain table descriptor validation only during testing scenarios, i.e,
when this knob is turned on. This is achieved by intercepting the
context at the conn_executor level to include a value that indicates
to the validation functions if extra validation should be performed.
By intercepting the context at this level, instead of somewhere closer
to the Validate calls, we avoid having to find and intercept the context
in all possible codepaths -- which was getting quite messy.

On the validation side, this patch adds two to be filled functions --
validateCrossReferencesIfTesting and validateTableIfTesting. We don't
validate cross references for mutable descriptors, so providing these
two functions allows us to preserve this pattern and cover both
mutable/immutable descriptors in testing only validation. The functions
are currently no-ops and will be filled in in upcoming patches.

Currently, the testing knob is turned on by default for all test
servers. If you're writing a test and don't want to opt into this
validation for some reason, there's a
DisableTestingDescriptorValidation on server args that can be set.

Release note: None

[cockroach-teamcity]

This change is 

[otan]

Reviewed 32 of 33 files at r1.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @ajwerner and @arulajmani)

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pkg/sql/catalog/tabledesc/structured.go, line 1434 at r1 (raw file):

// PerformTestingDescriptorValidation can be set as a value on a context to
// ensure testing specific descriptor validation happens.
var PerformTestingDescriptorValidation = testingDescriptorValidation(true)

super nit: i think this is nicer to read

var PerformTestingDescriptorValidation testingDescriptorValidation = true

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pkg/sql/logictest/logic.go, line 1262 at r1 (raw file):

				},
				//SQLExecutor: &sql.ExecutorTestingKnobs{
				//	TestingDescriptorValidation: true,

why is this commented out?

[arulajmani]

TFTR!

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @ajwerner and @otan)

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pkg/sql/catalog/tabledesc/structured.go, line 1434 at r1 (raw file):

Previously, otan (Oliver Tan) wrote…

super nit: i think this is nicer to read

var PerformTestingDescriptorValidation testingDescriptorValidation = true

Done.

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pkg/sql/logictest/logic.go, line 1262 at r1 (raw file):

Previously, otan (Oliver Tan) wrote…

why is this commented out?

My bad, I intended to remove this but instead left it commented out. This was from a previous approach where this descirptor validation was only for logictests, but in the new approach it's for all tests unless you opt out, making this knob here useless.

[arulajmani]

bors r=otan

[craig]

Build succeeded:

• GitHub CI (Cockroach)