Speed up syncing and creating symlink for compose-web/Dockerfile

ci/docker/compose-web/Dockerfile

@@ -24,4 +24,7 @@ RUN mkdir androidx-main
 WORKDIR  androidx-main
 RUN ~/bin/repo init -u https://android.googlesource.com/platform/manifest \
     -b androidx-main --partial-clone --clone-filter=blob:limit=10M
-RUN ~/bin/repo sync
+RUN ~/bin/repo sync -c --no-tags --no-clone-bundle -j4
+RUN ln -sf /androidx-main/tools/ /mnt/tools
+RUN ln -sf /androidx-main/prebuilts/ /mnt/prebuilts
+RUN ln -sf /androidx-main/external /mnt/external