Fix some missed opportunities for preInlineUnconditionally

There are two signficant changes here:

* Ticket #18815 showed that we were missing some opportunities for
  preInlineUnconditionally.  The one-line fix is in the code for
  GHC.Core.Opt.Simplify.Utils.preInlineUnconditionally, which now
  switches off only for INLINE pragmas.  I expanded
  Note [Stable unfoldings and preInlineUnconditionally] to explain.

* When doing this I discovered a way in which preInlineUnconditionally
  was occasionally /too/ eager.  It's all explained in
  Note [Occurrences in stable unfoldings] in GHC.Core.Opt.OccurAnal,
  and the one-line change adding markAllMany to occAnalUnfolding.

I also got confused about what NoUserInline meant, so I've renamed
it to NoUserInlinePrag, and changed its pretty-printing slightly.
That led to soem error messate wibbling, and touches quite a few
files, but there is no change in functionality.

I did a nofib run.  As expected, no significant changes.

        Program           Size    Allocs
----------------------------------------
         sphere          -0.0%     -0.4%
----------------------------------------
            Min          -0.0%     -0.4%
            Max          -0.0%     +0.0%
 Geometric Mean          -0.0%     -0.0%

I'm allowing a max-residency increase for T10370, which seems
very irreproducible. (See comments on !4241.)  There is always
sampling error for max-residency measurements; and in any case
the change shows up on some platforms but not others.

Metric Increase:
    T10370

1 files changed, 2 insertions, 2 deletions

diff --git a/compiler/GHC/Hs/Binds.hs b/compiler/GHC/Hs/Binds.hs
index a2d46d35ed..f5e973053a 100644
--- a/compiler/GHC/Hs/Binds.hs
+++ b/compiler/GHC/Hs/Binds.hs
@@ -1160,8 +1160,8 @@ ppr_sig (SpecSig _ var ty inl@(InlinePragma { inl_inline = spec }))
                                              (interpp'SP ty) inl)
     where
       pragmaSrc = case spec of
-        NoUserInline -> "{-# SPECIALISE"
-        _            -> "{-# SPECIALISE_INLINE"
+        NoUserInlinePrag -> "{-# SPECIALISE"
+        _                -> "{-# SPECIALISE_INLINE"
 ppr_sig (InlineSig _ var inl)
   = pragSrcBrackets (inl_src inl) "{-# INLINE"  (pprInline inl
                                    <+> pprPrefixOcc (unLoc var))