Switch TypeApplications to given extensions

[som-snytt]

Casual refactor to try newer features.

[som-snytt]

I prefer to assume it's yet another spurious test failure.

[info] Test run dotty.tools.pc.tests.hover.HoverTermSuite started
[info] Test dotty.tools.pc.tests.hover.HoverTermSuite.for-keyword started
Error:  Test dotty.tools.pc.tests.hover.HoverTermSuite.for-keyword failed: java.util.concurrent.CancellationException: null, took 10.636 sec
Error:      at java.util.concurrent.CompletableFuture.cancel(CompletableFuture.java:2276)
Error:      at scala.meta.internal.pc.CompilerAccess.onCompilerJobQueue$$anonfun$3$$anonfun$1(CompilerAccess.scala:231)
Error:      at java.util.concurrent.FutureTask.run(FutureTask.java:266)
Error:      at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
Error:      at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
Error:      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
Error:      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
Error:      at java.lang.Thread.run(Thread.java:748)

There is an infrastructure problem with so many recent failures.

pc tests are inherently flaky if they are reactive. It would be nice to have tiers of unit tests, functional tests (integration), and liveliness tests that might time out but which would be run in a quiescent environment maybe once a day.