fix #10511: compare enumvalues in provably disjoint

[bishabosha]

this also shortcuts comparing object refs without looking at their supertype

fixes #10511

[bishabosha]

I have also tested transitivity of passing aliases to singleton enum values, such as this:

val t: True.type = True
val f: False.type = False

val t1: Not[f.type] = t // transitivity
val f1: Not[t.type] = f // transitivity

Edit: this has been prevented from running in the FromTasty test due to aparrently different reduction of match types with that option

[OlivierBlanvillain]

It's nice that Singleton helps inference here, the following compiles as expected:

not(True): False.type

Although it's a bit fragile:

val vrais = True
not(vrais): False.type // error, we lost the singleton type...

[bishabosha]

yeah its true with enums a user must do a lot of work to avoid the widening but thats something hopefully we can tune based on feedback without ruining bincompat

[OlivierBlanvillain]

I think this PR should also update the docs, the diff LGTM otherwise.

It wouldn't be sounds to compare singleton types in the general case, but as far as I can tell it's fine to do for enums because value cases are guaranteed to point to a different object.

[bishabosha]

I've updated the match-types doc

[bishabosha]

so FromTastyTest for pos/i10511.scala failed at -Ycheck:readTasty due to the match type Not[(f1 : Not[(t : (Bool.True : Bool))])] not reducing under -from-tasty, I've added an exception to FromTastyTest for now

[bishabosha]

it is possible to get the -from-tasty -Ycheck:readTasty for Not[(f1 : Not[(t : (Bool.True : Bool))])] to pass if I call sym.info.normalized in a recursive version of isEnumValueOrModule but it is probably best to do that at unpickling time when we see a match type:

def isEnumValueOrModule(ref: TermRef): Boolean =
  val sym = ref.termSymbol
  sym.isAllOf(EnumCase, butNot=JavaDefined)
    || sym.is(Module)
    || (sym.info.normalized match
        case tp: TermRef => isEnumValueOrModule(tp)
        case tp => false)

or get Ycheck to normalise types before checking bounds