Missing warning on ignored parsing attributes on type alias

[bbannier]

The parser currently accepts parsing attributes on type alias declarations, e.g., this alias is accepted:

type Addr = addr &ipv4;

Using this alias triggers an error though:

type X = unit {
    : Addr; # ERROR: address field must come with either &ipv4 or &ipv6 attribute
};

This is due to us accepting the attribute on the alias, but ignoring it (correctly since here &ipv4 is not an proper attribute for a type, but only a field). In this case this is just confusing, but could make it to silently introduce bugs if attributes like e.g., &requires or &max-size. See e.g., #1845 (comment) where this cause confused a user.

I feel we should outright reject such attributes with a diagnostic.