Convert lib/FileHandle.t to use of Test::More; provide descriptions.

Previously, file used hand-coded 'print "ok"' statements and no tests had
descriptions (a.k.a. labels or names).  Convert to use of Test::More functions
and provide descriptions for all individual tests.

Previously, file used global variables extensively and did not 'use strict'
(except 'use strict subs').  The globals have been converted to lexicals
where appropriate and the file now runs fully under strictures.  Other
than that, no attempt was made to improve the design of the file or the
quality of the tests.  (That can be done in a later RT, if desired.)

Thanks to Peter Martini for guidance and Dagfinn Ilmari Mannsåker for guidance
and code review on list.

For: RT #118883