improve: filter as a plugin (#4255)

src/core/plugins/filter/index.js

@@ -0,0 +1,9 @@
+import opsFilter from "./opsFilter"
+
+export default function() {
+  return {
+    fn: {
+      opsFilter
+    }
+  }
+}

src/core/plugins/filter/opsFilter.js

@@ -0,0 +1,3 @@
+export default function(taggedOps, phrase) {
+  return taggedOps.filter((tagObj, tag) => tag.indexOf(phrase) !== -1)
+}