Add test for interpolating over zoom (#2008)

Fixes #1899

Author: kevinschaul

src/style-spec/feature_filter/feature_filter.test.ts

@@ -19,6 +19,7 @@ describe('filter', () => {
         compileTimeCheck(['case', ['all', ['has', 'point_count'], ['<', ['get', 'point_count'], 3]], ['get', 'cluster_routes'], '']);
         compileTimeCheck(['interpolate', ['linear'], ['get', 'point_count'], 2, 18.0, 10, 24.0]);
         compileTimeCheck(['interpolate', ['linear'], ['get', 'point_count'], 2, ['/', 2, ['get', 'point_count']], 10, ['*', 4, ['get', 'point_count']]]);
+        compileTimeCheck(['interpolate', ['linear'], ['zoom'], 16, ['literal', [0, 1]], 17, ['literal', [0, 2]]]);
         compileTimeCheck(['case', ['has', 'point_count'], ['interpolate', ['linear'], ['get', 'point_count'], 2, 18.0, 10, 24.0], 12.0]);
         compileTimeCheck([
             'case',