feat: locale support for date filter, #567 (#723)

test/stub/date.ts

@@ -0,0 +1,16 @@
+import { LiquidDate } from '../../src/util'
+
+const locale = Intl.DateTimeFormat().resolvedOptions().locale
+
+export class DateWithTimezone extends LiquidDate {
+  constructor (init: string, timezone: number) {
+    super(init, locale)
+    this.getTimezoneOffset = () => timezone
+  }
+}
+
+export class TestDate extends LiquidDate {
+  constructor (v: any) {
+    super(v, locale)
+  }
+}