Run the tests unconditionally and skip if the shaper is not available.
This fixes distcheck (https://github.com/harfbuzz/harfbuzz/pull/3504)
and shows SKIP for these tests instead of ignoring them.
For builds from release tarballs, the tests fail in the DirectWrite and
Uniscribe tests when these platform shapers are enabled, since the data files
were not found in the source tree, when building with Meson at least.
Fix this by dist'ing the platform shaper test data files.
Test that both NFC and NFD input produces identical results for fonts
that used composed fonts internally (Amiri here) and fonts that
decompose internally (Noto Nastaliq Urdu here) and that for the former
composed forms are used.
See https://github.com/harfbuzz/harfbuzz/issues/3179
David Corbett
Khaled Hosny
Chun-wei Fan
Behdad Esfahbod
Simon Cozens