prettier: don't depend on system node being available

ts/format.sh

@@ -1,4 +1,7 @@
 # this is a hack to invoke prettier directly from Bazel
+node=$(pwd)/$1
+node_dir=$(dirname $node)
+export PATH="$node_dir:$PATH"
 (cd "${BUILD_WORKSPACE_DIRECTORY}" && node_modules/.bin/prettier \
     --config .prettierrc --write \
     $BUILD_WORKING_DIRECTORY )

ts/prettier.bzl

@@ -30,4 +30,6 @@ def prettier(name = "format", **kwargs):
     native.sh_binary(
         name = name,
         srcs = ["format.sh"],
+        args = ["$(location @nodejs//:node_bin)"],
+        data = ["@nodejs//:node_bin"],
     )