[resubmitted] Fix #9061: Treat type F <: [X] => G like type F[X] <: G.

[smarter]

Accidentally merged in #9084, reverted and resubmitted because the community build started failing:

2020-05-30T15:04:52.6008148Z [info] Set current project to effpi (in build file:/__w/dotty/dotty/community-build/community-projects/effpi/)
2020-05-30T15:04:58.4723186Z [error] -- [E007] Type Mismatch Error: /__w/dotty/dotty/community-build/community-projects/effpi/src/main/scala/ActorDSL.scala:118:13 
2020-05-30T15:04:58.4723812Z [error] 118 |    pdsl.rec(RecA)(beh >> pdsl.loop(RecA))
2020-05-30T15:04:58.4724173Z [error]     |             ^^^^
2020-05-30T15:04:58.4724507Z [error]     |             Found:    effpi.actor.dsl.RecA.type
2020-05-30T15:04:58.4724861Z [error]     |             Required: effpi.process.RecVar[A]
2020-05-30T15:04:59.5859259Z [error] -- [E007] Type Mismatch Error: /__w/dotty/dotty/community-build/community-projects/effpi/src/main/scala/ActorDSL.scala:118:36 
2020-05-30T15:04:59.5859978Z [error] 118 |    pdsl.rec(RecA)(beh >> pdsl.loop(RecA))
2020-05-30T15:04:59.5860354Z [error]     |                                    ^^^^
2020-05-30T15:04:59.5860740Z [error]     |                                   Found:    effpi.actor.dsl.RecA.type
2020-05-30T15:04:59.5861157Z [error]     |                                   Required: effpi.process.RecVar[A]
2020-05-30T15:05:00.0746454Z [error] two errors found
2020-05-30T15:05:00.1342256Z [error] (Compile / compileIncremental) Compilation failed

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[odersky]

@alcestes I had to disable effpi in the community build since it started failing with the errors shown above after a variance soundness hole was fixed. Could you take a look to see whether you can fix it so that it compiles again?

[smarter]

I'm not sure if the problem is really in effpi, I can get it to compile with the following commit: smarter/effpi@5270291. Dotty is misinterpreting the type bounds without explicit kinding, so either we should disallow them, or support them properly.

[odersky]

I think we should disallow these bounds. But that should be in a separate PR since that will require more code to be changed. Can you add the changes to effpi so that we can close this one?