Add `:constraint_handler` and `Ecto.Adapters.SQL.Constraint` #1916

Job	Run time
unittest (1.17.2, 25.0.4)	18s
postgres integration test (1.14.5-erlang-23.3.4.9-alpine-3.16.9, 16.2-alpine, 1)	1m 41s
postgres integration test (1.14.5-erlang-23.3.4.9-alpine-3.16.9, 9.6-alpine, 1)	1m 47s
unittest (1.17.2, 27.0.1, lint)	21s
mysql integration test (1.14.5-erlang-23.3.4.9-alpine-3.16.9, 8.0)	2m 4s
mysql integration test (1.14.5-erlang-23.3.4.9-alpine-3.16.9, 5.7)	1m 59s
mssql integration test (1.14.5-erlang-23.3.4.9-alpine-3.16.9, 2019)	2m 11s
postgres integration test (1.14.5-erlang-23.3.4.9-alpine-3.16.9, 11.11-alpine, 1)	1m 48s
postgres integration test (1.14.5-erlang-23.3.4.9-alpine-3.16.9, 16.2-alpine, 4)	1m 42s
postgres integration test (1.14.5-erlang-23.3.4.9-alpine-3.16.9, 9.5-alpine, 1)	1m 44s
mssql integration test (1.14.5-erlang-23.3.4.9-alpine-3.16.9, 2022)	2m 11s
	17m 46s

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