build: Add dist script

This script will vendor the Rust dependencies
of the app so that our tarballs can be built
offline.

build-aux/meson/dist-vendor.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+export DIST="$1"
+export SOURCE_ROOT="$2"
+
+cd "$SOURCE_ROOT"
+mkdir "$DIST"/.cargo
+cargo vendor | sed 's/^directory = ".*"/directory = "vendor"/g' > $DIST/.cargo/config
+# Move vendor into dist tarball directory
+mv vendor "$DIST"