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.

src/backend/utils/adt/quote.c

@@ -76,17 +76,17 @@ quote_literal_internal(char *dst, const char *src, size_t len)
 Datum
 quote_literal(PG_FUNCTION_ARGS)
 {
-	text	   *t = PG_GETARG_TEXT_P(0);
+	text	   *t = PG_GETARG_TEXT_PP(0);
 	text	   *result;
 	char	   *cp1;
 	char	   *cp2;
 	int			len;
 
-	len = VARSIZE(t) - VARHDRSZ;
+	len = VARSIZE_ANY_EXHDR(t);
 	/* We make a worst-case result area; wasting a little space is OK */
 	result = (text *) palloc(len * 2 + 3 + VARHDRSZ);
 
-	cp1 = VARDATA(t);
+	cp1 = VARDATA_ANY(t);
 	cp2 = VARDATA(result);
 
 	SET_VARSIZE(result, VARHDRSZ + quote_literal_internal(cp2, cp1, len));