Recover from TypeErrors in isErroneous

[odersky]

Fixes #15293 (hopefully)

[odersky]

How I fixed it:

That one was simple. Looking at the stacktrace:

at dotty.tools.dotc.core.Types$NamedType.argDenot(Types.scala:2326)
        at dotty.tools.dotc.core.Types$NamedType.fromDesignator$1(Types.scala:2240)
        at dotty.tools.dotc.core.Types$NamedType.computeDenot(Types.scala:2258)
        at dotty.tools.dotc.core.Types$NamedType.denot(Types.scala:2213)
        at dotty.tools.dotc.core.Types$NamedType.info(Types.scala:2201)
        at dotty.tools.dotc.core.TypeApplications$.typeParams$extension(TypeApplications.scala:185)
        at dotty.tools.dotc.core.Types$AppliedType.tyconTypeParams(Types.scala:4456)
        at dotty.tools.dotc.core.Types$TypeAccumulator.foldOver(Types.scala:6004)
        at dotty.tools.dotc.core.Types$ExistsAccumulator.apply(Types.scala:6095)
        at dotty.tools.dotc.core.Types$Type.existsPart(Types.scala:452)
        at dotty.tools.dotc.core.Types$Type.isErroneous(Types.scala:359)
        at scala.meta.internal.pc.printer.MetalsPrinter.tpe(MetalsPrinter.scala:67)

Something went wrong in isErroneous which was called from MetalsPrinter. isErroneous should always default to true instead of throwing an exception. So I put in a handler for the thrown TypeError exception.

Why not put in a more sweeping handler for all exceptions? Since that one could hide bugs that I might want to see. I'd like to verify that an exception is plausible and does not hide a larger problem before it gets caught and ignored in isErroneous.

[odersky]

Going to merge it now, so that it makes it into 3.2