[LANGUAGE idea] Never give a parse error!

[Felienne]

Discussion #3450 (rightly!) points out that the parse errors are bad! Why do we even ever show them?

This is more of an aspirational message to myself, but I think we should really strive to never need a parse error but to always have an error production to fall back on (which @akseron is already working on in part!)

[Felienne]

@akseron is working on this, I will document the related issues here too so we know what is connected

[Felienne]

Once related issue is (newly made) #4780

Another one is B of this one: #4350

[Felienne]

And this one: #4355

[Felienne]

In this (sadly very long and thus poorly linkable) comment, another suggestion is made for Parse errors, to change the phrasing from "that is not allowed" to "this confuses Hedy", I like that!

#3967 (comment)