meson: try vapoursynth-script first

Older versions ship separate `vapoursynth-script.pc` and
`vapoursynth.pc`, we want to use `script` one. Try it first, if not
available use `vapoursynth`, which is the only one new version ships.

meson.build

@@ -783,7 +783,10 @@ if features['uchardet']
     dependencies += uchardet
 endif
 
-vapoursynth = dependency('vapoursynth', version: '>= 56', required: get_option('vapoursynth'))
+vapoursynth = dependency('vapoursynth-script', version: '>= 56', required: false)
+if not vapoursynth.found()
+    vapoursynth = dependency('vapoursynth', version: '>= 56', required: get_option('vapoursynth'))
+endif
 features += {'vapoursynth': vapoursynth.found()}
 if features['vapoursynth']
     dependencies += vapoursynth.partial_dependency(compile_args: true, includes: true)