As Trac #10047 points out, a quasi-quotation [n|...blah...|] is supposed
to behave exactly like $(n "...blah...").  But it doesn't!  This was outright
wrong: quasiquotes were being run even inside brackets.

Now that TH supports both typed and untyped splices, a quasi-quote is properly
regarded as a particular syntax for an untyped splice. But apart from that
they should be treated the same.  So this patch refactors the handling of
quasiquotes to do just that.

The changes touch quite a lot of files, but mostly in a routine way.
The biggest changes by far are in RnSplice, and more minor changes in
TcSplice.  These are the places where there was real work to be done.
Everything else is routine knock-on changes.

* No more QuasiQuote forms in declarations, expressions, types, etc.
  So we get rid of these data constructors
    * HsBinds.QuasiQuoteD
    * HsExpr.HsSpliceE
    * HsPat.QuasiQuotePat
    * HsType.HsQuasiQuoteTy

* We get rid of the HsQuasiQuote type altogether

* Instead, we augment the HsExpr.HsSplice type to have three
  consructors, for the three types of splice:
    * HsTypedSplice
    * HsUntypedSplice
    * HsQuasiQuote
  There are some related changes in the data types in HsExpr near HsSplice.
  Specifically: PendingRnSplice, PendingTcSplice, UntypedSpliceFlavour.

* In Hooks, we combine rnQuasiQuoteHook and rnRnSpliceHook into one.
  A smaller, clearer interface.

* We have to update the Haddock submodule, to accommodate the hsSyn changes