feat: where filter, working on #118

doc: https://shopify.github.io/liquid/filters/where/
ruby impl: https://github.com/Shopify/liquid/blob/14cd011cb5eef042af192ad5294c8f0e1ae89f06/lib/liquid/standardfilters.rb

test/integration/builtin/filters/array.ts

@@ -64,4 +64,28 @@ describe('filters/array', function () {
       return test('{{"" | uniq | join: ","}}', '')
     })
   })
+  describe('where', function () {
+    it('should support filter by property value', function () {
+      return test(`{% assign kitchen_products = products | where: "type", "kitchen" %}
+Kitchen products:
+{% for product in kitchen_products -%}
+- {{ product.title }}
+{% endfor %}`, `
+Kitchen products:
+- Spatula
+- Garlic press
+`)
+    })
+    it('should support filter truthy property', function () {
+      return test(`{% assign available_products = products | where: "available" %}
+Available products:
+{% for product in available_products -%}
+- {{ product.title }}
+{% endfor %}`, `
+Available products:
+- Coffee mug
+- Boring sneakers
+`)
+    })
+  })
 })