[no-release-notes] Engine test framework for Doltgres

[zachmu]

This PR introduces two major changes to how enginetests are defined and run in Dolt:

1. New Harness interface to abstract Dolt-specific setup logic and make the same test logic usable by Doltgres
2. Pull test methods defined in Dolt into their own exported methods to be consumed by Doltgres, similar to the contract between GMS and Dolt

There will be more changes necessary as we get these working in Doltgres, but this lets us run all the Dolt enginetests on Doltgres.

[coffeegoddd]

@zachmu DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
8419789	ok	5937457

version	total_tests
8419789	5937457

correctness_percentage
100.0

[coffeegoddd]

@coffeegoddd DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
bfae6a5	ok	5937457

version	total_tests
bfae6a5	5937457

correctness_percentage
100.0

[max-hoffman]

LGTM, I am assuming this mostly moving interfaces public/abstracting the DoltHarness. If there are novel code/tests I should be inspecting more closely lmk.

[coffeegoddd]

@zachmu DOLT

comparing_percentages
100.000000 to 100.000000

version	result	total
85956dc	ok	5937457

version	total_tests
85956dc	5937457

correctness_percentage
100.0