Debug QL installation

[aegilops]

Run debug steps to check existing QL installation, and suggest and do fixes.

• check that there is just one QL library in the search path.
• ensure that the QL library and CLI binary are compatible versions.
• check that the CLI binary is properly in the VSCode settings.
• check that the workplace has the QL library added to it.
• check that a .yml file for a QL query has updated legacy libraryPathDependencies to dependencies key if using a CLI version above v2.6.0:
  https://codeql.github.com/docs/codeql-cli/about-ql-packs/
• check we can extract a database for some basic test code - Python, JavaScript, Java, C, C#
  • only try if we have a compiler/interpreter for the language
  • check that the extracted DB contains what we'd expect (files, functions, classes)