More printf de-duplication.

Fix the 'j' (intmax_t/uintmax_t) length qualifier in the wide
variant. (With new tests that fail without this fix.)

Fix a typo in the wide support for intmax_t*, which isn't testable because
%n is disabled on Android (and will be removed in a later cleanup pass).

Also move the public vfprintf/vfwprint functions into stdio.cpp.

Bug: http://b/67371539
Test: ran tests
Change-Id: Ib003599b1e9cb789044a068940b59e447f2cb7cb