fea-rs should reject name table statements for certain ids

[cmyr]

Noted by @khaledhosny:

Names defined in the feature file override those already in the name table. This what feaLib does, and I believe this is what makeotf does as well (though it does not allow overriding name IDs 2 and 6, or at least that what the spec says, I haven’t tested it recently).

Originally posted by @khaledhosny in #1133 (comment)

from testing neither fonttools nor fea-rs are respecting this little corner of the spec; afdko is rejecting ids 1 through 6 (not quite what the spec says, but the spec text clearly has a little thunko because it says 2 and 6 but names six ids; I opened an issue against the spec)

(this is very low priority in any case)

[khaledhosny]

makeotf has a command line switch to allow these name IDs except for 2 and 6, so these are the two it does not support at all. But even Adobe considers this a makeotf implementation detail and not something other implementations need to do. Even if this is not the case, I don’t see what can be gained from enforcing arbitrary limits like this.