Fix bogus smartcast on enum entry members

Previously, enum entries were treated by the data-flow subsystem similar
to other class/singletons. As a consequence, calls like
'Enum.ENTRY.property' had IdentifierInfo of 'property'.

However, specially for enum entries, descriptor of 'property' is one and
the same for all entries. It means that from the data-flow point of
view, 'Enum.ONE.property' and 'Enum.TWO.property' are *one and the same
data-flow values*.

It could obviously lead to some bogus smartcasts, so this commit
introduces separate IdentifierInfo.EnumEntry and uses it to build proper
qualified values.

^KT-20772 Fixed

compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt

@@ -84,6 +84,7 @@ enum class LanguageFeature(
     NoConstantValueAttributeForNonConstVals(KOTLIN_1_3, kind = BUG_FIX),
     NormalizeConstructorCalls(KOTLIN_1_3),
     StrictJavaNullabilityAssertions(KOTLIN_1_3, kind = BUG_FIX),
+    SoundSmartcastForEnumEntries(KOTLIN_1_3, kind = BUG_FIX),
 
     RestrictReturnStatementTarget(KOTLIN_1_4, kind = BUG_FIX),
     ProperIeee754Comparisons(sinceVersion = null, defaultState = State.DISABLED, kind = BUG_FIX),