schemahcl: added `yamldecode`/`yamlencode` functions #2047

Job	Run time
generate-cmp	45s
integration	38s
cli	3m 11s
lint	36s
unit (1.22)	9s
dialect-integration / integration-maria102	2m 55s
dialect-integration / integration-maria107	2m 52s
dialect-integration / integration-maria103	2m 54s
dialect-integration / integration-cockroach	2m 57s
dialect-integration / integration-mysql56	2m 53s
dialect-integration / integration-mysql57	2m 55s
dialect-integration / integration-mysql8	3m 5s
dialect-integration / integration-postgres10	3m 12s
dialect-integration / integration-postgres11	3m 9s
dialect-integration / integration-postgres12	3m 6s
dialect-integration / integration-postgres13	3m 21s
dialect-integration / integration-postgres14	3m 9s
dialect-integration / integration-postgres15	3m 27s
dialect-integration / integration-postgres-ext-postgis	3m 9s
dialect-integration / integration-sqlite	2m 29s
dialect-integration / integration-tidb5	3m 28s
dialect-integration / integration-tidb6	3m 28s
	57m 48s

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