Remove redundant iteration in EntitySelectionTree merging algorithm #977

Job	Run time
Cocoapods Integration Tests - macOS	25s
Codegen Test Configurations - macOS	5m 47s
Run swift build for SPM packages (apollo-ios)	45s
changes	5s
Run swift build for SPM packages (apollo-ios-codegen)	1m 6s
Run swift build for SPM packages (apollo-ios-pagination)	1m 11s
Run Tuist Generation	1m 26s
Verify Frontend Bundle Latest - macOS	24s
Apollo Integration Tests - macOS	0s
Apollo Unit Tests - macOS	14s
Codegen CLI Unit Tests - macOS	2m 32s
Codegen Lib Unit Tests - macOS	3m 32s
ApolloPagination Unit Tests - macOS	11s
	17m 38s

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