Devcontainer support (#4748)

devcontainers are a convenient way to provide users a reproducible
build environment. It is currently supported by Visual Studio Code,
Visual Studio and IntelliJ.

When the user opens the verilator repo in VSCode with the standard
devcontainer extension installed, VSCode will ask the user if they
want to reopen in the devcontainer, then build the Docker image as per
our definition and then restart VSCode 'remotely' attached to the
Docker container.

More information:
https://code.visualstudio.com/docs/devcontainers/containers

Also:

- zlibc is missing on Debian-based systems now
- Add non-root user to Dockerfile and make default

.devcontainer/devcontainer.json

@@ -0,0 +1,8 @@
+{
+	"name": "Verilator Build Environment",
+
+	"build": {
+        "dockerfile": "../ci/docker/buildenv/Dockerfile"
+    }
+
+}

ci/docker/buildenv/Dockerfile

@@ -8,6 +8,16 @@
 
 FROM ubuntu:22.04
 
+# Create the user
+RUN groupadd verilator \
+    && useradd -g verilator -m verilator -s /bin/bash \
+    && apt-get update \
+    && apt-get install --no-install-recommends -y sudo \
+    && apt-get clean \
+    && rm -rf /var/lib/apt/lists/* \
+    && echo verilator ALL=\(root\) NOPASSWD:ALL > /etc/sudoers.d/verilator \
+    && chmod 0440 /etc/sudoers.d/verilator
+
 RUN apt-get update \
     && DEBIAN_FRONTEND=noninteractive \
        apt-get install --no-install-recommends -y \
@@ -33,7 +43,6 @@ RUN apt-get update \
                         perl \
                         python3 \
                         wget \
-                        zlibc \
                         zlib1g \
                         zlib1g-dev \
     && apt-get clean \
@@ -52,6 +61,8 @@ COPY build.sh /tmp/build.sh
 
 ENV VERILATOR_AUTHOR_SITE=1
 
+USER verilator
+
 WORKDIR /work
 
 ENTRYPOINT [ "/tmp/build.sh" ]