Add end to end extension to language server testing

[jpogran]

Organizes and adds the following tests:

• Completions
  • Root document completion
  • Completion for a local module sources (prefix ./)
  • Completion for inputs of a local module
  • Completion of the variable name inside the tfvars file
• Go to Definition
  • Go-to-definition on a local module source
  • Go-to-definition on a module input
  • Go-to-definition on a var.something reference
  • Go-to-definition on the variable name inside tfvars
• References
  • Find module references
  • Find references on the variable block
• Symbols
  • Basic symbol return
• Hover
  • core schema provides docs
• Code actions
  • formats the document

Migrate to vscode-cli

Removes the original test runner infrastructure and replaces it with vscode-cli, which is the new recommend testing approach. This helps simplify executing VS Code API tests and helps ensure terraform-ls is up and initialized before running tests.

Notes

We now have two test folders: src/test and test/specs, along with two fixtures folders: test/fixtures and testFixtures. This does not address combining them or moving them because the wdio tsconfig/npm packaging conflicts with the vscode ones.

[dbanck]

Really good work ❤️ ! I think these integration tests will help us a lot in the future!

I added some suggestions on how to reduce the potential flakiness and how to bring back the mocha helpers.

[dbanck]

Awesome!

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