fix(linux): restore VAAPI hardware decode and AV1 software fallback in the bundled libmpv

Hardware decoding stopped working for Linux users on 2.13.0 (Fedora 44
report): every source decodes in software, and AV1 plays black video with
audio. Two defects in the pinned libmpv build.

First, mpv's meson 'drm' feature silently disabled itself because the CI
builder lacks libdisplay-info, and every VAAPI path that does not depend
on a display server is derived from it: vaapi-copy's standalone render-node
device (the path 2.12.1 worked on) and the GL dmabuf interop for direct
vaapi. With only the Wayland VA provider compiled in, a machine whose
Wayland VA display fails to initialize has no fallback, and vaapi-copy
has an empty provider list - every source lands on software decoding.
Pin -Ddrm=enabled, -Dvaapi-drm=enabled, -Degl=enabled and
-Dvaapi-wayland=enabled, and add libdisplay-info-dev to the CI package
lists, so a missing piece fails the build instead of shipping silent
software decode.

Second, the bundled static FFmpeg has no AV1 software decoder: its native
av1 codec is hardware-accelerated only, so once hwdec fails there is no AV1
path at all - every packet errors, video hits EOF, the plane goes black
while audio keeps playing. Pin dav1d 1.5.4 (both VideoLAN remotes agree on
the tag object and root commit), build it static before ffmpeg, and pass
--enable-libdav1d.

The build-plan stub test now asserts the hwdec feature flags, the dav1d
static build, and ffmpeg's libdav1d. Verified in an ubuntu:24.04 container
with the production flag sets: meson reports drm, vaapi-drm, vaapi-wayland,
egl and dmabuf-interop-gl enabled, and ffmpeg configures CONFIG_LIBDAV1D=yes
with the AV1 VAAPI hwaccel.

close #1874

scripts/verify_runtime_inputs.py

@@ -13,7 +13,7 @@ from typing import Any
 
 HEX_256 = re.compile(r"^[0-9a-f]{64}$")
 HEX_COMMIT = re.compile(r"^[0-9a-f]{40}$")
-NATIVE_NAMES = {"ffmpeg", "shaderc", "libplacebo", "mpv", "simdutf"}
+NATIVE_NAMES = {"dav1d", "ffmpeg", "shaderc", "libplacebo", "mpv", "simdutf"}
 BINDING_ARTIFACTS = {
     "pigeons/messages.dart",
     "android/src/main/kotlin/dev/fluttercommunity/plus/wakelock/WakelockPlusMessages.g.kt",
@@ -103,8 +103,12 @@ def _validate_native(root: Path, errors: list[str]) -> None:
         elif kind == "git":
             ref = value.get("ref")
             commit = value.get("commit")
-            if not isinstance(ref, str) or ref != f"v{version}":
-                errors.append(f"{label}.ref: must be v{version}")
+            # dav1d tags releases as bare versions ("1.5.4"); the other pinned
+            # Git inputs tag them "v{version}". Either way the ref is verified
+            # against the recorded commit, which is the actual pin.
+            expected_ref = version if name == "dav1d" else f"v{version}"
+            if not isinstance(ref, str) or ref != expected_ref:
+                errors.append(f"{label}.ref: must be {expected_ref}")
             if not isinstance(commit, str) or HEX_COMMIT.fullmatch(commit) is None:
                 errors.append(f"{label}.commit: must be a lowercase full Git commit")
         else:
@@ -139,6 +143,7 @@ def _validate_native(root: Path, errors: list[str]) -> None:
         "native-inputs.json",
         'download_verified "$FFMPEG_URL" "$FFMPEG_SHA256"',
         'download_verified "$MPV_URL" "$MPV_SHA256"',
+        '"$DAV1D_URL" "$DAV1D_REF" "$DAV1D_COMMIT"',
         '"$SHADERC_URL" "$SHADERC_REF" "$SHADERC_COMMIT"',
         '"$LIBPLACEBO_URL" "$LIBPLACEBO_REF" "$LIBPLACEBO_COMMIT"',
         'git submodule update --init --recursive',