Move native builds to wholphin-extensions (#1172)

## Description
This PR moves the native components (ffmpeg decoder, av1 decoder, &
`libmpv`) to https://github.com/damontecres/wholphin-extensions. They
can be retrieved as gradle dependencies now.

This allows for contributors to more easily include these extensions
when building Wholphin locally.

There are no user facing changes in this PR.

Note: the kotlin code for interfacing with `libmpv`, ie `MPVLib` &
`MpvPlayer`, is still in this repo for now.

### Related issues
Related to #828

### Testing
Emulator

## Screenshots
N/A

## AI or LLM usage
None

.github/actions/native-build/action.yml

@@ -1,82 +0,0 @@
-name: "Native build"
-description: "Performs native builds"
-inputs:
-  cache:
-    description: "Whether to use the cache or not"
-    required: true
-runs:
-  using: "composite"
-  steps:
-    - name: Load ffmpeg module cache
-      id: cache_ffmpeg_module
-      if: ${{ inputs.cache }}
-      uses: actions/cache/restore@v5
-      with:
-        path: |
-          app/libs
-        key: ${{ runner.os }}-ffmpeg-${{ hashFiles('**/libs.versions.toml', '**/scripts/ffmpeg/build_ffmpeg_decoder.sh') }}
-    - name: Load libmpv module cache
-      id: cache_libmpv_module
-      if: ${{ inputs.cache }}
-      uses: actions/cache/restore@v5
-      with:
-        path: |
-          app/src/main/libs
-        key: ${{ runner.os }}-libmpv-${{ hashFiles('**/scripts/mpv/*.sh', '**/scripts/mpv/include/*', '**/scripts/mpv/scripts/*', 'app/src/main/jni/*') }}
-    - name: Install dependencies
-      if: steps.cache_ffmpeg_module.outputs.cache-hit != 'true' || steps.cache_libmpv_module.outputs.cache-hit != 'true'
-      shell: bash
-      run: |
-        python -m pip install --upgrade pip
-        pip install jsonschema jinja2
-        sudo apt update
-        sudo apt install -y build-essential autoconf pkg-config libtool ninja-build unzip wget meson nasm
-
-
-# ffmpeg
-    - name: Build ffmpeg decoder
-      id: ffmpeg-decoder
-      if: steps.cache_ffmpeg_module.outputs.cache-hit != 'true'
-      shell: bash
-      run: |
-        cd scripts/ffmpeg
-        ./build_ffmpeg_decoder.sh "${{ env.ANDROID_SDK_ROOT }}/ndk/${{ env.NDK_VERSION }}"
-    - name: Save ffmpeg module cache
-      id: cache_ffmpeg_module_save
-      uses: actions/cache/save@v5
-      with:
-        path: |
-          app/libs
-        key: ${{ steps.cache_ffmpeg_module.outputs.cache-primary-key }}
-
-# libmpv
-    - name: Get libmpv dependencies
-      if: steps.cache_libmpv_module.outputs.cache-hit != 'true'
-      shell: bash
-      run: |
-        cd scripts/mpv
-        ./get_dependencies.sh
-    - name: Build libmpv dependencies
-      if: steps.cache_libmpv_module.outputs.cache-hit != 'true'
-      shell: bash
-      run: |
-        cd scripts/mpv
-        ./buildall.sh --clean --arch arm64 mpv
-        ./buildall.sh mpv
-        cd ../..
-        env PREFIX32="$(realpath scripts/mpv/prefix/armv7l)" PREFIX64="$(realpath scripts/mpv/prefix/arm64)" ndk-build -C app/src/main -j
-
-    - name: Setup jniLibs
-      shell: bash
-      run: |
-        cd app/src/main
-        mkdir -p jniLibs
-        cp -r libs/* jniLibs
-        #ln -s libs jniLibs
-    - name: Save libmpv module cache
-      id: cache_libmpv_module_save
-      uses: actions/cache/save@v5
-      with:
-        path: |
-          app/src/main/libs
-        key: ${{ steps.cache_libmpv_module.outputs.cache-primary-key }}