Fix reordering of bidi text in an isolate inside an override

Fix reordering of bidi text in an isolate inside an override

* src/bidi.c (bidi_resolve_explicit): Override the orig_type value
of FSI with either LRI or RLI, as determined by the first strong
directional character in the isolate.  This prevents failure to
isolate when the FSI...PDI text is inside a directional override.
(Bug#22786)