Add workflow for copying compiled artifacts to 0x/contract-artifacts (#1842)

The contract artifacts should remain as standard compiler output during development. Fields should only be removed/added prior to being published in `@0x/contract-artifacts`. This PR adds the `yarn transform` script to `@0x/contract-artifacts` to facilitate this. 

Going forward, `abi-gen-templates` will have to support both standard artifacts and modified artifacts if they diverge, since the templates are used for `contract-artifacts`/`abi-gen-wrappers` (modified artifact) *and* development in all the `contracts/*` packages (standard artifact).

This PR makes the following changes to `contract-artifacts`:
- remove `evm.bytecode.linkReferences` from all artifacts
- remove `evm.deployedBytecode` and `sourceTreeHashHex` from Coordinator artifact
- prettify all artifacts (whitespace only changes)

packages/contract-artifacts/src/transform.ts

@@ -0,0 +1,50 @@
+import { deleteNestedProperty, logUtils } from '@0x/utils';
+import * as fs from 'fs';
+
+export const REQUIRED_PROPERTIES: string[] = [
+    'schemaVersion',
+    'contractName',
+    'compilerOutput.evm.bytecode.object',
+    'compilerOutput.abi',
+];
+
+export const FORBIDDEN_PROPERTIES: string[] = [
+    'compilerOutput.evm.bytecode.sourceMap',
+    'compilerOutput.evm.bytecode.opcodes',
+    'compilerOutput.evm.bytecode.linkReferences',
+    'compilerOutput.evm.deployedBytecode',
+    'compilerOutput.evm.assembly',
+    'compilerOutput.evm.legacyAssembly',
+    'compilerOutput.evm.gasEstimates',
+    'compilerOutput.evm.methodIdentifiers',
+    'compilerOutput.metadata',
+    'compilerOutput.userdoc',
+    'sourceCodes',
+    'sources',
+    'sourceTreeHashHex',
+];
+
+function removeForbiddenProperties(inputDir: string, outputDir: string): void {
+    const filePaths = fs
+        .readdirSync(inputDir)
+        .filter(filename => filename.indexOf('.json') !== -1)
+        .map(filename => `./${inputDir}/${filename}`);
+
+    for (const filePath of filePaths) {
+        const artifact = JSON.parse(fs.readFileSync(filePath).toString()) as { [name: string]: any };
+        for (const property of FORBIDDEN_PROPERTIES) {
+            deleteNestedProperty(artifact, property);
+        }
+        fs.writeFileSync(filePath.replace(inputDir, outputDir), JSON.stringify(artifact));
+    }
+}
+
+if (require.main === module) {
+    const inputDir = process.argv[2];
+    const outputDir = process.argv[3] !== undefined ? process.argv[3] : inputDir;
+    logUtils.log(`Deleting forbidden properties from artifacts in ${inputDir}. Output to ${outputDir}`);
+    if (!fs.existsSync(`./${outputDir}`)) {
+        fs.mkdirSync(`./${outputDir}`);
+    }
+    removeForbiddenProperties(inputDir, outputDir);
+}