Use wrappers of PG_DETOAST_DATUM_PACKED() more.

This makes almost all core code follow the policy introduced in the
previous commit.  Specific decisions:

- Text search support functions with char* and length arguments, such as
  prsstart and lexize, may receive unaligned strings.  I doubt
  maintainers of non-core text search code will notice.

- Use plain VARDATA() on values detoasted or synthesized earlier in the
  same function.  Use VARDATA_ANY() on varlenas sourced outside the
  function, even if they happen to always have four-byte headers.  As an
  exception, retain the universal practice of using VARDATA() on return
  values of SendFunctionCall().

- Retain PG_GETARG_BYTEA_P() in pageinspect.  (Page images are too large
  for a one-byte header, so this misses no optimization.)  Sites that do
  not call get_page_from_raw() typically need the four-byte alignment.

- For now, do not change btree_gist.  Its use of four-byte headers in
  memory is partly entangled with storage of 4-byte headers inside
  GBT_VARKEY, on disk.

- For now, do not change gtrgm_consistent() or gtrgm_distance().  They
  incorporate the varlena header into a cache, and there are multiple
  credible implementation strategies to consider.

contrib/intarray/_int_op.c

@@ -200,9 +200,9 @@ Datum
 sort(PG_FUNCTION_ARGS)
 {
 	ArrayType  *a = PG_GETARG_ARRAYTYPE_P_COPY(0);
-	text	   *dirstr = (fcinfo->nargs == 2) ? PG_GETARG_TEXT_P(1) : NULL;
-	int32		dc = (dirstr) ? VARSIZE(dirstr) - VARHDRSZ : 0;
-	char	   *d = (dirstr) ? VARDATA(dirstr) : NULL;
+	text	   *dirstr = (fcinfo->nargs == 2) ? PG_GETARG_TEXT_PP(1) : NULL;
+	int32		dc = (dirstr) ? VARSIZE_ANY_EXHDR(dirstr) : 0;
+	char	   *d = (dirstr) ? VARDATA_ANY(dirstr) : NULL;
 	int			dir = -1;
 
 	CHECKARRVALID(a);