refactor: move emit from callback to helper file function (#704)

* Change emit from callback to helpers file function

* Update docs, remove commented code, improve type sig

quartz/plugins/emitters/helpers.ts

@@ -0,0 +1,19 @@
+import path from "path"
+import fs from "fs"
+import { BuildCtx } from "../../util/ctx"
+import { FilePath, FullSlug, joinSegments } from "../../util/path"
+
+type WriteOptions = {
+  ctx: BuildCtx
+  slug: FullSlug
+  ext: `.${string}` | ""
+  content: string
+}
+
+export const write = async ({ ctx, slug, ext, content }: WriteOptions): Promise<FilePath> => {
+  const pathToPage = joinSegments(ctx.argv.output, slug + ext) as FilePath
+  const dir = path.dirname(pathToPage)
+  await fs.promises.mkdir(dir, { recursive: true })
+  await fs.promises.writeFile(pathToPage, content)
+  return pathToPage
+}