wasm-emscripten: update emscripten SDK to 3.1.55

Upgrades the toolchain to clang 19 since our last image version.

vlc-debian-wasm-emscripten/Dockerfile

 FROM debian:bookworm-20231009-slim
 
-ENV IMAGE_DATE=202211290000
+ENV IMAGE_DATE=202403080000
 
 ARG VIDEOLAN_UID=499
-ARG EMSDK_VERSION=3.1.47
+ARG EMSDK_VERSION=3.1.55
 ARG CORES=8
 
 ENV PATH=/opt/tools/bin:$PATH