Simplify re-identification in `FlatFileSchemaResolver` #5387

Job	Run time
test (macos-latest, clang, clang++, static, sh, macos/llvm)	4m 18s
test (macos-latest, clang, clang++, shared, sh)	2m 8s
test (macos-latest, gcc-13, g++-13, static, sh)	9m 3s
test (ubuntu-latest, clang, clang++, static, sh, linux/llvm)	5m 6s
test (ubuntu-latest, gcc, g++, static, sh, linux/gcc)	8m 6s
test (ubuntu-latest, clang, clang++, shared, sh)	4m 17s
test (ubuntu-latest, gcc, g++, shared, sh)	3m 53s
test (windows-latest, static, pwsh, windows/msvc)	7m 22s
test (windows-latest, shared, pwsh)	7m 1s
test (ubuntu-latest, clang, clang++, static, sh, -DJSONTOOLKIT_ADDRESS_SANITIZER:BOOL=ON)	4m 49s
test (ubuntu-latest, clang, clang++, static, sh, -DJSONTOOLKIT_UNDEFINED_SANITIZER:BOOL=ON)	4m 48s
	1h 0m 51s

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