e350c357 (#40228) introduced a subtle bug: it switched the flags to an
alias, dropping `SymbolFlags.Property` --- and that makes
`symbolIsValue()` get to the `resolveAlias(symbol)` call, which leads to
`getPropertyOfType()` with`resolved.callSignatures`+`constructSignatures`
being `undefined`. So initialize them in `setStructuredTypeMembers`
before calling `getNamedMembers()`.
Fixes#42350
