Sanitize target name before resolving

[sephialaureenciaa]

↪️ Pull Request

Closes #9001

Before this PR, parcel will throw an error when target name contains slash. To fix this, we wrap targetName with encodeJSONKeyComponent so that the slash gets encoded properly.

💻 Examples

    "/dist/server_commonjs": {
      "isLibrary": true,
      "source": "src/index.ts",
      "optimize": false,
      "context": "node",
      "outputFormat": "commonjs",
      "distDir": "dist/server/commonjs"
    }

Previously, this error would pop up:
Error: Cannot use 'in' operator to search for 'key' in undefined

✔️ PR Todo

• Added/updated unit tests for this change
• Filled out test instructions (In case there aren't any unit tests)
• Included links to related issues/PRs