preparser: use of an external process for preparsing

Updated 2025/04/16

This MR improves media parsing stability by isolating the preparser in a dedicated external process (vlc-preparser), using a JSON-based IPC protocol.

• External preparser process:

  • Creates vlc-preparser as a standalone process to handle parsing requests.
  • Uses JSON messages for IPC between VLC core and vlc-preparser process.
  • Read request on STDIN and print responce in STDOUT.
  • Send big attachments (picture_t or input_attachment_t) in binary just after the JSON.

• New preparser backend system:

  • Implements module-like interface for the preparser.
  • Maintains compatibility with existing preparser API.
  • Adds a boolean in the vlc_preparser_cfg struture to choose between internal preparser or with the external process.
  • Updates playlist and the medialib thumbnailer to use the external process.

• Serialization framework:

  • Implements JSON serialization/deserialization module for preparser_msg structure.

• Other:

  • Change vlc_pipe for windows.
  • Add es_vec in input_item_Copy function.
  • Add a input_item_Update function that use the data of one input_item to update an other one. (Like input_item_Copy but using the same input_item instead of creating a new one)
  • Add a input_item_node_Copy to copy all the input_item_node tree. (The inner items are just held)
  • Add getter for meta value.

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