ci: Add Hardhat tooling integration test (#516)

## Description

Adds a CI workflow that builds a small Hardhat project with
`hardhat-polkadot`, exercising the standard JSON interface between
`resolc` and `hardhat-polkadot` end-to-end.

## Resolved Issues

Closes #514

tooling-projects/hardhat/erc20/verify-compiler-output.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+
+# Asserts that the compiled project contains the expected compiler output.
+# Run from the project's root.
+
+set -euxo pipefail
+
+shopt -s nullglob
+build_info_files=(artifacts/build-info/*.json)
+if [[ ${#build_info_files[@]} -ne 1 ]]; then
+  echo "expected exactly one build-info file under artifacts/build-info/, found ${#build_info_files[@]}" >&2
+  exit 1
+fi
+
+build_info=${build_info_files[0]}
+contract='.output.contracts["contracts/MyToken.sol"].MyToken'
+source='.output.sources["contracts/MyToken.sol"]'
+
+jq -er "$contract.evm.bytecode.object"         "$build_info" | grep -q '^50564d'
+jq -er "$contract.evm.deployedBytecode.object" "$build_info" | grep -q '^50564d'
+jq -e "$contract.evm.methodIdentifiers         | length > 0" "$build_info" > /dev/null
+jq -e "$contract.abi                           | length > 0" "$build_info" > /dev/null
+jq -e "$contract.storageLayout.storage         | length > 0" "$build_info" > /dev/null
+jq -e "$contract.metadata                      | length > 0" "$build_info" > /dev/null
+jq -e "$source.ast                             | length > 0" "$build_info" > /dev/null
+jq -e '.output.sources                         | length > 1' "$build_info" > /dev/null
+
+echo "all checks passed"