Simplify MetaPlaylist Manifest loading by relying on the same code th…

…an other transports

I was PoCing protocol-detection when initially parsing the Manifest, so
application developers wouldn't e.g. have to tell to us that they want
to play "dash".

While doing that, I noticed that all transports had close to the same
logic for Manifest fetching. Only differences I've seen are:

  - DASH may add integrity checks if the `checkManifestIntegrity` option
    is set

  - DASH may ask the browser to obtain the response as an ArrayBuffer
    (and not as a default JS string) if it is probable that we will rely
    on the WASM MPD parser

  - the `local` transport throws if no custom `manifestLoader` is
    declared.

As such, those differences look minor and straightforward enough so the
corresponding logic can be factorized into e.g. a single parameterized
`createManifestLoader` function.

This was already done for DASH and Smooth, but I don't know why we
didn't use it for the experimental MetaPlaylist feature. This commit
fixes this.

We could also use it for the experimental `local` transport in the
future, though I'm unsure of how we could generically make sense of its
peculiar rule (no real loading).

src/transports/metaplaylist/pipelines.ts

@@ -45,7 +45,7 @@ import type {
   ITransportOptions,
   ITransportPipelines,
 } from "../types";
-import generateManifestLoader from "./manifest_loader";
+import generateManifestLoader from "../utils/generate_manifest_loader";
 
 /**
  * Get base - real - content from an offseted metaplaylist content.
@@ -113,9 +113,13 @@ function getMetaPlaylistPrivateInfos(segment: ISegment): IMetaPlaylistPrivateInf
 export default function (options: ITransportOptions): ITransportPipelines {
   const transports: Partial<Record<string, ITransportPipelines>> = {};
 
-  const manifestLoader = generateManifestLoader({
-    customManifestLoader: options.manifestLoader,
-  });
+  const manifestLoader = generateManifestLoader(
+    {
+      customManifestLoader: options.manifestLoader,
+    },
+    "text",
+    null,
+  );
 
   // remove some options that we might not want to apply to the
   // other streaming protocols used here