Registry auto discovery in LSP

[lucacasonato]

We should reintroduce the registry auto discovery we had in extension v2. Here is how it works:

When the LSP identifies an origin in a specifier for the first time it will try to fetch the well-known manifest for that origin. If a manifest is found, a message pops up asking the user if they want to enable import completions for that origin. If they press Yes the origin will be added to the deno.suggest.imports.hosts list and set to true. If they press no the origin will be added to that list, and set to false.

Example:

Auto discovery can be disabled with the deno.suggest.imports.autoDiscovery: false option. It is set to true by default.