fix(tsconfig): Set rootDir to centralize compilation output

Problem: TypeScript was creating .js and .js.map files next to source files
in new-extension/ and old-extension/ directories because tsconfig included
files from outside the project (../src/**/*.ts) without setting rootDir.

Solution: Add 'rootDir: ".."' to comparison-test-harness/tsconfig.json
This tells TypeScript the common ancestor of all included files, allowing
it to properly map the directory structure into outDir.

Before: adapter.js created at comparison-test-harness/new-extension/adapter.js
After:  adapter.js created at comparison-test-harness/out/comparison-test-harness/new-extension/adapter.js

Author: JohannesHoppe

comparison-test-harness/tsconfig.json

@@ -9,6 +9,7 @@
     "forceConsistentCasingInFileNames": true,
     "resolveJsonModule": true,
     "moduleResolution": "node",
+    "rootDir": "..",
     "outDir": "./out",
     "experimentalDecorators": true,
     "emitDecoratorMetadata": true,