Expose the used Nim installation dir

[jmgomez]

In order for the nimlangserver to be able to use the right nimsuggest version we must expose it via nimble. The idea here is to expose the solved Nim version or the one used to build the packages. So later on, the nimlangserver can ask nimble for the right nimsuggest.

In order to accomplish this, we should also add a capabilities flag, like nimsuggest has. So the lsp can know if the current nimble supports it.

[jmgomez]

Exposes the nimdir in the dump command: #1221