simplify extendSchemaImpl with mapSchemaConfig #1815

Job	Run time
ci / Build 'denoDist' artifact	22s
ci / Build 'npmDist' artifact	40s
ci / Build website	1m 7s
ci / Check for commonly ignored files	5s
ci / Check health of package-lock.json file	20s
ci / Run CodeQL security scan	1m 26s
ci / Run fuzzing tests	41s
ci / Run integration tests	1m 40s
ci / Lint source files	1m 3s
ci / Run tests on Node v16	32s
ci / Run tests on Node v18	33s
ci / Run tests on Node v19	31s
Deploy to `deno` branch	0s
Deploy to `npm` branch	0s
	9m 0s

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