release-22.2: tests: support float approximation in roachtest query comparison utils

[rharding6373]

Backport 2/2 commits from #106552.

/cc @cockroachdb/release

---

tests, logictest, floatcmp: refactor comparison test util functions

This commit moves some float comparison test util functions from
logictest into the floatcmp package. It also moves a query result
comparison function from the tlp file to query_comparison_util in the
tests package.

This commit also marks roachtests as testonly targets.

Epic: none

Release note: None

tests: support float approximation in roachtest query comparison utils

Before this change unoptimized query oracle tests would compare results
using simple string comparison. However, due to floating point precision
limitations, it's possible for results with floating point to diverge
during the course of normal computation. This results in test failures
that are difficult to reproduce or determine whether they are expected
behavior.

This change utilizes existing floating point comparison functions used
by logic tests to match float values only to a specific precision. Like
the logic tests, we also have special handling for floats and decimals
under the s390x architecture (see #63244). In order to avoid costly
comparisons, we only check floating point precision if the naiive string
comparison approach fails and there are float or decimal types in the
result.

Epic: None
Fixes: #95665

Release note: None

Release justification: Test only change that will reduce incorrect test failures from approximate float values in randomized testing.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• 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.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[michae2]

Reviewed 9 of 9 files at r1, 6 of 6 files at r2, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @rharding6373)

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pkg/testutils/floatcmp/floatcmp.go line 126 at r2 (raw file):

	var expPower, actPower int
	expected, expPower = math.Frexp(expected)
	actual, actPower = math.Frexp(actual)

Same comment here (also need to backport #107490 at the same time).

[rharding6373]

I'm going to open a new backport with both PRs.