LibWeb: Add a script to run Web Platform Tests

Introduce very initial and basic support for running Web Platform Tests
for Ladybird. This change includes simple bash script that currently
works only on Debian and could run tests with patched runner.

For now script to run WPT is not integrated in CI.

There is also a bunch of metadata required to run WPT. To avoid
introducing thousands of files in the initial commit for now it is
limited to run only css/CSS2/floats tests subdirectory.

Tests/LibWeb/WPT/run.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+
+set -eo pipefail
+
+if [ -z "$SERENITY_SOURCE_DIR" ]
+then
+    echo "SERENITY_SOURCE_DIR is not set. Exiting."
+fi
+
+# NOTE: WPT runner assumes Ladybird, WebContent and WebDriver are available in $PATH.
+export PATH="${SERENITY_SOURCE_DIR}/Build/lagom/bin:${SERENITY_SOURCE_DIR}/Meta/Lagom/Build/bin:${PATH}"
+
+# Install dependencies.
+sudo apt-get install -y git python3 python3-pip python3-venv libssl-dev
+
+# Ensure a `python` binary exists
+sudo apt-get install -y python-is-python3
+
+# Clone patched web-platform-tests repository
+git clone --depth 10000 https://github.com/web-platform-tests/wpt.git
+
+# Switch to the commit that was used to generate tests expectations. Requires periodic updates.
+(cd wpt; git checkout 4c27189ed2db4ddad8e727d4ea9ae8329c3e1672)
+
+# Apply WPT patch with Ladybird runner
+(cd wpt; git apply ../ladybird_runner.patch)
+
+# Update hosts file
+./wpt/wpt make-hosts-file | sudo tee -a /etc/hosts
+
+# Extract metadata.txt into directory with expectation files expected by WPT runner
+./concat-extract-metadata.py --extract metadata.txt metadata
+
+# Run tests.
+./wpt/wpt run ladybird --include-manifest include.ini --metadata ./metadata --manifest ./MANIFEST.json