Add `flatMapOrKeep` to `Monad` #2696

Job	Run time
Scalafix (ubuntu-latest, temurin@8)	58s
Submit Dependencies	0s
Generate Site (ubuntu-latest, temurin@17)	2m 13s
Build and Test (ubuntu-latest, 2.12, temurin@8, rootJS)	1m 29s
Validate Steward Config (ubuntu-latest, temurin@11)	13s
Build and Test (ubuntu-latest, 2.12, temurin@8, rootJVM)	1m 25s
Build and Test (ubuntu-latest, 2.12, temurin@8, rootNative)	1m 27s
Build and Test (ubuntu-latest, 2.13, temurin@8, rootJS)	1m 29s
Build and Test (ubuntu-latest, 2.13, temurin@8, rootJVM)	1m 21s
Build and Test (ubuntu-latest, 2.13, temurin@8, rootNative)	1m 29s
Build and Test (ubuntu-latest, 2.13, temurin@17, rootJVM)	1m 37s
Build and Test (ubuntu-latest, 2.13, graalvm@17, rootJVM)	1m 37s
Build and Test (ubuntu-latest, 3, temurin@8, rootJS)	1m 19s
Build and Test (ubuntu-latest, 3, temurin@8, rootJVM)	1m 20s
Build and Test (ubuntu-latest, 3, temurin@8, rootNative)	1m 27s
Publish Artifacts	0s
	19m 24s

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