Improvements to JavaScript analysis

Changes to code extraction

Asynchronous generator methods are now parsed correctly and no longer cause a spurious syntax error.
Files in node_modules and bower_components folders are no longer extracted by default. If you still want to extract files from these folders, you can add the following filters to your lgtm.yml file (or add them to existing filters):
```
extraction:
  javascript:
    index:
      filters:
        - include: "**/node_modules"
        - include: "**/bower_components"
```
Additional Flow syntax is now supported.
Recognition of CommonJS modules has improved. As a result, some files that were previously extracted as global scripts are now extracted as modules.
Top-level await is now supported.
Bugs were fixed in how the TypeScript extractor handles default-exported anonymous classes and computed-instance field names.