Fixes #248

Overview

• Introduce new top level item for displaying the dotnet Local Tools
• Use dotnet tool list --local to discover locally installed tools (this operation is actually very fast, i think it just reads the manifest file)
• New comands: "Add local tool", "Remove local tool". "Update local tools version"
• The UX for adding/updating/removing is very similar to how packages are managed

Installation of local tools requires a local manifest file to exist, else you'll get the following error:

❯ dotnet tool install --local "Cake.Tool" --version "3.0.0"
Cannot find a manifest file.
For a list of locations searched, specify the "-d" option before the tool name.
If you intended to install a global tool, add `--global` to the command.
If you would like to create a manifest, use `dotnet new tool-manifest`, usually in the repo root directory.

I decided to not manage this in the extension as it's obvious to the user what needs to be done to resolve the error.

Screencast