Defer errors in derived instances

Fixes Trac #9576.  Turned out to be pretty easy.
Do not discard insoluble Derived constraints

This is preparing for a fix to Trac #9612. The idea is that insoluble
constraints are nice solid errors that we should not discard before
we have a chance to report them.  So TcRnTypes.dropDerivedWC now
keeps insoluble Derived constrains, and instead TcSimplify.solve_wanteds
filters them out

We get somewhat better error message for kind-equality failures too.

A slight downside is that to avoid *duplicate* kind-equality failures
when we float a kind-incompatible equality (e.g.  alpha:* ~ Int#),
I've disabled constraint-floating when there are insolubles.  But that
in turn makes a handful of error messages a little less informative;
good examples are mc21, mc22, mc25.  But I am re-jigging the
constraint floating machinery in another branch, which will make this
go back to the way it was before.
Wibble to implicit-parameter error message
Improve error messages from functional dependencies

Reponding to Trac #9612:

 * Track the CtOrigin of a Derived equality, arising from a
   functional dependency

 * And report it clearly in the error stream

This relies on a previous commit, in which I stop dropping Derived
insolubles on the floor.
Two improved error messages

I'm not quite sure why these have improved following the previous
four commits, but I'm quite happy about it
Complain about illegal type literals in renamer, not parser

A premature complaint was causing Trac #9634.  Acutally this
change also simplifies the lexer and eliminates duplication.
(The renamer was already making the check, as it happens.)