Converted `test-extensions-unit.bat` to javascript to add a small QoL improvement that I think people will find useful: specifying which extension(s) you want to run tests for instead of commenting out lines of a script.
In addition to existing behavior being mostly preserved (node test-extensions-unit.js defaults to running all unit tests), you can specify one or more:
```
node test-extensions-unit.js sql-database-projects
node test-extensions-unit.js sql-database-projects schema-compare
```