sql: move end-to-end and KV tests and common test code to a new package sql/tests

[knz]

Visible changes here:

• common test code in sql/tests
• high-level SQL tests in sql/tests/highlevel
• SQL/KV tests in sql/tests/sqlkv

[cockroach-teamcity]

This change is 

[knz]

Rebased after merge of #20106. PTAL.

[jordanlewis]

re: highlevel - is there a reason why these tests can't just live in tests? It's already clear to me from the package structure that things inside of ./pkg/sql/tests are "high level" sql tests.

Same question for sqlkv. Why not just put them in tests?

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Reviewed 14 of 15 files at r1, 25 of 27 files at r2, 10 of 10 files at r3, 12 of 12 files at r4.
Review status: all files reviewed at latest revision, 2 unresolved discussions, all commit checks successful.

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pkg/sql/tests/sqlkv/benchmark_test.go, line 13 at r4 (raw file):

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
// implied. See the License for the specific language governing
// permissions and limitations under the License.

All of our benchmark tests files are called bench_test.go except for this one.

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pkg/sql/tests/sqlkv/main_test.go, line 1 at r4 (raw file):

// Copyright 2015 The Cockroach Authors.

2017?

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Comments from Reviewable

[knz]

Merged the commits and put the files in a single package sql/tests, as we discussed. PTAL.

[knz]

Review status: 27 of 36 files reviewed at latest revision, 2 unresolved discussions.

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pkg/sql/tests/kv_test.go, line 13 at r4 (raw file):

Previously, jordanlewis (Jordan Lewis) wrote…

All of our benchmark tests files are called bench_test.go except for this one.

Reverted.

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pkg/sql/tests/sqlkv/main_test.go, line 1 at r4 (raw file):

Previously, jordanlewis (Jordan Lewis) wrote…

2017?

Done.

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Comments from Reviewable

[jordanlewis]

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Reviewed 4 of 15 files at r3, 4 of 16 files at r4, 19 of 19 files at r5.
Review status: all files reviewed at latest revision, all discussions resolved, all commit checks successful.

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Comments from Reviewable

[knz]

TFYR!