[meson] Add first regression test to FreeType

* tests/README.md: documentation explaining how to
  build and run the tests with the Meson build.

* tests/scripts/download-test-fonts.sh: Simple script
  to download test font files to the 'tests/data/'
  folder.

* meson.build, meson_options.txt, tests/meson.build:
  Add 'tests' option to enable building and running the
  test programs, disabled by default.

* tests/issue-1063/main.c: Simple regression test to
  exhibit issue 1063.

* .gitignore: Ignore the content of the tests/data/
  folder for now.

meson_options.txt

@@ -35,6 +35,11 @@ option('harfbuzz',
                + ' If available, many glyphs not directly addressable'
                + ' by a font\'s character map will be hinted also.')
 
+option('tests',
+  type: 'feature',
+  value: 'disabled',
+  description: 'Enable FreeType unit and regression tests.')
+
 option('brotli',
   type: 'feature',
   value: 'auto',