Enable basic CMake language services

[gcampbell-msft]

This PR accomplishes the following:

• Removes the dependency on the third party twxs.cmake extension. Thanks @twxs for your work in that extension!
• Add support into our extension for the following:
  • Quick Info for built-in modules, variables, properties, and functions.
  • Completions for built-in modules, variables, properties, and functions.

This does this by including JSON files in our repository that house information for language services and we load these on activation of the extension. This enhances the performance of providing completions and quick info information.

The main implementation points in this PR:

• Bundling the language services json assets into the vsix (gulpfile.js, etc.)
• Integrating with the VS Code Language Service API to implement quick hover and completions (src/languageServices)

Fixes #3559. Fixes #534. Fixes #3560