[node] Enable npm to build mapbox-gl-native package from source

- Allow node bindings to be built if git submodules cannot be checked out
 - Made geojsonvt a mason package instead of a git submodule
 - Use globally installed mason if it cannot be checked out via git submodules

test/test.gypi

@@ -95,6 +95,7 @@
       'libraries': [
         '<@(libuv_static_libs)',
         '<@(sqlite_static_libs)',
+        '<@(geojsonvt_static_libs)',
       ],
       'variables': {
         'cflags_cc': [
@@ -102,6 +103,8 @@
           '<@(opengl_cflags)',
           '<@(boost_cflags)',
           '<@(sqlite_cflags)',
+          '<@(geojsonvt_cflags)',
+          '<@(variant_cflags)',
         ],
         'ldflags': [
           '<@(libuv_ldflags)',