Streamlines devcontainer Dockerfile and adds fontconfig (#26281)

* Streamlines devcontainer Dockerfile and adds fontconfig

fontconfig enables running pulse rendering tests in a devcontainer
with a headless JVM. The Dockerfile has been streamlined and a comment
added to explain the additional requirement.

* Adds rlwrap (for clj command)

.devcontainer/Dockerfile

 FROM mcr.microsoft.com/vscode/devcontainers/java:11
 
-RUN apt-key adv --refresh-keys --keyserver keyserver.ubuntu.com\
-  && apt-get update && export DEBIAN_FRONTEND=noninteractive \
-  && apt-get -y install --no-install-recommends yarn
+# Set up nodesource, install node, yarn, fontconfig for static viz, rlwrap for dev ergonomics
 
-RUN curl -fsSL https://deb.nodesource.com/setup_14.x | bash
-RUN apt-get update && apt-get -y install --no-install-recommends nodejs
+RUN ( curl -fsSL https://deb.nodesource.com/setup_14.x | bash ) \
+  && export DEBIAN_FRONTEND=noninteractive \
+  && apt-key adv --refresh-keys --keyserver keyserver.ubuntu.com \
+  && apt-get update && apt-get -y install --no-install-recommends nodejs yarn rlwrap fontconfig
 
-RUN curl -O https://download.clojure.org/install/linux-install-1.11.0.1100.sh \
-  && bash ./linux-install-1.11.0.1100.sh
+# install Clojure
+RUN curl https://download.clojure.org/install/linux-install-1.11.0.1100.sh | bash