Enforce conversion method return type & redefine Comparable #26679

Job	Run time
Cancel Previous Runs	4s
Engine (GraalVM CE) (linux, x86_64)	20m 53s
Engine (GraalVM CE) (windows, x86_64)	27m 9s
Engine (GraalVM CE) (macos, x86_64)	58m 12s
JVM Tests (GraalVM CE) (linux, x86_64)	1h 32m 5s
JVM Tests (GraalVM CE) (macos, x86_64)	1h 59m 56s
JVM Tests (GraalVM CE) (windows, x86_64)	1h 42m 4s
Standard Library Tests (GraalVM CE) (linux, x86_64)	20m 45s
Standard Library Tests (GraalVM CE) (macos, x86_64)	28m 31s
Standard Library Tests (GraalVM CE) (windows, x86_64)	25m 59s
Verify License Packages (linux, x86_64)	1m 7s
	8h 16m 45s

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