Add experimental MPV player backend (#161)

Experimental MPV player backend

Related to #14, #22, & #85

You can switch to MPV in advanced settings and toggle using hardware
decoding or not.

This uses code and buildscripts from
https://github.com/mpv-android/mpv-android, plus other third party
libraries to build MPV

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

@@ -0,0 +1,79 @@
+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@v4
+      with:
+        path: |
+          app/libs
+        key: ${{ runner.os }}-ffmpeg-${{ hashFiles('**/libs.versions.toml', '**/scripts/ffmpeg/build_ffmpeg_decoder.sh') }}
+    - 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@v4
+      with:
+        path: |
+          app/libs
+        key: ${{ steps.cache_ffmpeg_module.outputs.cache-primary-key }}
+
+    - name: Load libmpv module cache
+      id: cache_libmpv_module
+      if: ${{ inputs.cache }}
+      uses: actions/cache/restore@v4
+      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_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
+    - 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@v4
+      with:
+        path: |
+          app/src/main/libs
+        key: ${{ steps.cache_libmpv_module.outputs.cache-primary-key }}