tests/test-gendoc-zh_TW.t

requirements: introduce constants for `shared` and `relshared` requirements

We add them to `WORKING_DIR_REQUIREMENTS` too as they should be stored in
`.hg/requires` and have information about the type of working copy.

Differential Revision: https://phab.mercurial-scm.org/D8926

#require docutils gettext

  $ $TESTDIR/check-gendoc zh_TW
  checking for parse errors