Support loading Zstandard-compressed ROMs (#1667)

This is different from the archive support in that the compressed ROMs
are standalone files, rather than archives, making it possible to use
them exactly as if they were regular ROMs, while saving a bunch of space
on disk. This is supported both for DS and GBA ROMs, though given GBA
ROMs' generally small size it's mostly useful for the former.

.github/workflows/build-ubuntu-aarch64.yml

@@ -33,7 +33,7 @@ jobs:
         rm /etc/apt/sources.list
         mv /etc/apt/sources.list{.new,}
         apt update
-        DEBIAN_FRONTEND=noninteractive apt install -y {gcc-10,g++-10,pkg-config}-aarch64-linux-gnu {libsdl2,qtbase5,qtbase5-private,qtmultimedia5,libslirp,libarchive}-dev:arm64 cmake extra-cmake-modules dpkg-dev
+        DEBIAN_FRONTEND=noninteractive apt install -y {gcc-10,g++-10,pkg-config}-aarch64-linux-gnu {libsdl2,qtbase5,qtbase5-private,qtmultimedia5,libslirp,libarchive,libzstd}-dev:arm64 zstd:arm64 cmake extra-cmake-modules dpkg-dev
     - name: Configure
       shell: bash
       run: |

.github/workflows/build-ubuntu.yml

@@ -19,7 +19,7 @@ jobs:
       run: |
         sudo rm -f /etc/apt/sources.list.d/dotnetdev.list /etc/apt/sources.list.d/microsoft-prod.list
         sudo apt update
-        sudo apt install cmake extra-cmake-modules libcurl4-gnutls-dev libpcap0.8-dev libsdl2-dev qt5-default qtbase5-private-dev qtmultimedia5-dev libslirp0 libslirp-dev libarchive-dev --allow-downgrades
+        sudo apt install cmake extra-cmake-modules libcurl4-gnutls-dev libpcap0.8-dev libsdl2-dev qt5-default qtbase5-private-dev qtmultimedia5-dev libslirp0 libslirp-dev libarchive-dev zstd libzstd-dev --allow-downgrades
     - name: Create build environment
       run: mkdir ${{runner.workspace}}/build
     - name: Configure