feat: tablerowloop object

See: https://www.rubydoc.info/gems/liquid/Liquid/TablerowloopDrop

src/drop/forloop-drop.ts

@@ -0,0 +1,34 @@
+import { Drop } from './drop'
+
+export class ForloopDrop extends Drop {
+  protected i: number = 0
+  length: number
+  constructor (length: number) {
+    super()
+    this.length = length
+  }
+  next () {
+    this.i++
+  }
+  index0 () {
+    return this.i
+  }
+  index () {
+    return this.i + 1
+  }
+  first () {
+    return this.i === 0
+  }
+  last () {
+    return this.i === this.length - 1
+  }
+  rindex () {
+    return this.length - this.i
+  }
+  rindex0 () {
+    return this.length - this.i - 1
+  }
+  valueOf () {
+    return JSON.stringify(this)
+  }
+}