OverlappingFieldsCanBeMergedRule: Fix performance degradation #1610

Job	Run time
Diff content of NPM package	1m 40s
ci / Lint source files	1m 20s
ci / Check for commonly ignored files	6s
ci / Build website	3m 9s
ci / Check health of package-lock.json file	33s
ci / Measure test coverage	52s
ci / Run fuzzing tests	49s
ci / Run integration tests	1m 59s
ci / Run tests on Node v12	31s
ci / Run tests on Node v14	24s
ci / Run tests on Node v16	36s
ci / Run tests on Node v17	57s
ci / Build 'denoDist' artifact	59s
ci / Build 'npmDist' artifact	1m 0s
	14m 55s

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