Link to docs for functions

[dbanck]

Context

With the introduction of functions, we now show a description and parameter information for all available functions. It would be helpful to also link to the docs because they include examples and a longer description.

The link can appear right below the description.

Docs for functions are available for different Terraform versions, e.g.

• https://developer.hashicorp.com/terraform/language/v1.3.x/functions/list (v1.3.x)
• https://developer.hashicorp.com/terraform/language/functions/list (latest)

Proposal

• Research a way to build stable URLs to function docs
• Add the link to docs to HoverAtPos for functions
• Explore if it makes sense to include the link on completion too
• Explore if it makes sense to include the link on signature help too