[red-knot] Change Type::member to return a Result and rename it to try_member

[MichaReiser]

Description

Similar to Type::try_call, try_iterate, try_bool, ..., member should be renamed to try_member and return Result.

• I don't think it should be LookupResult: Instead, it should be a result specific to Type::member because we may want to preserve additional error information for better diagnostics that isn't relevant when doing other symbol lookups. But I might be wrong here
• I don't think try_member should return a Symbol because it behaves slightly different from all other type methods in that it doesn't necessarily consider a possibly unbound symbol as an error (but it probably is one for most type checking code).

We could offer helper methods to easily convert a Result<Type, MemberError> to a Result<Type, LookupError> or Symbol (e.g. implement From for Result<Type, LookupError> so that the try operator "just works").