decoder: Use glycin for decoding SVGs as well

Part-of: <https://gitlab.gnome.org/GNOME/loupe/-/merge_requests/267>

Cargo.toml

@@ -16,8 +16,10 @@ disable-glycin-sandbox = []
 anyhow = { version = "1.0.66", features = ["backtrace"] }
 arc-swap = "1.6.0"
 async-channel = "1.8.0"
+async-std = "1.12.0"
 env_logger = "0.10.0"
 futures = "0.3.25"
+glycin = "0.1.0-beta.1"
 gvdb-macros = "0.1.6"
 indexmap = "2.0.0"
 kamadak-exif = "0.5.5"
@@ -26,10 +28,6 @@ log = "0.4.17"
 once_cell = "1.16.0"
 url = "2.3.1"
 
-# decoders
-rsvg = { git = "https://gitlab.gnome.org/GNOME/librsvg.git", rev = "81b58cc1368ab10f6de3439c8b1276c40b8d4286" }
-glycin = "0.1.0-beta.0"
-
 [dependencies.ashpd]
 version = "0.5.0"
 features = ["gtk4"]