ffmpeg: add option to use the opencore amr nb/wb decoder instead of built-in amr decoder

[hwse]

Summary

Changes to recipe: ffmpeg

Motivation

This pull request allows users to enable the opencore amr decoder in ffmpeg. The internal amr wideband/narrowband decoder lacks some features and suggests to use opencore-amr (see here: https://github.com/FFmpeg/FFmpeg/blob/8272d34377b24e52de0492fbc2e1d74efcdff248/libavcodec/amrnbdec.c#L989C47-L989C64 ).

Details

• I added a option to enable opencore amr: with_opencore_amr
  • default is off
  • if enabled it adds a dependency to the opencore-amr package
  • also the internal amr decoder is disabled with this option
• when using opencore-amr we need to pass the --enable-version3 flag to upgrade to (L)GPL version 3
  • the license of opencore-amr is not compatible with LGPL 2.1, but LGPL 3.0
  • see here: https://github.com/FFmpeg/FFmpeg/blob/8272d34377b24e52de0492fbc2e1d74efcdff248/LICENSE.md?plain=1#L110
  • this is achieved using another new option: with_lgpl_version_3
  • also i added the (L)GPL version 3 to the license attribute
  • i am not sure if the with_lgpl_version_3 option is the best way to model this flag. A alternative could be to add the --enable-version3 flag if opencore-amr is enabled

---

• Read the contributing guidelines
• Checked that this PR is not a duplicate: list of PRs by recipe
• Tested locally with at least one configuration using a recent version of Conan

[CLAassistant]

All committers have signed the CLA.

[hwse]

Related Issue: #26308

[KepptnKool]

Changes look good

[thedavidhk]

The changes look good to me.