LSP: don't add registries to deno.suggest.imports.hosts that don't have a manifest

[lucacasonato]

Just typing out an import slowly results in a bunch of hosts added to .vscode/settings.json:

{
  "deno.enable": true,
  "deno.lint": true,
  "deno.unstable": false,
  "deno.suggest.imports.hosts": {
    "https://deno.land": true,
    "https://x.nest.land": true,
    "https://crux.land": true,
    "https://x.lcas.dev": true,
    "https://cdn.skypack.dev": false,
    "https://esm.sh": false,
    "https://skypack.": false,
    "https://cdn..sh": false,
    "https://e": false,
    "https://esm": false,
    "https://esm,.": false,
    "https://esm.": false,
    "https://esm.s": false
  }
}

If an origin does not provide a manifest, we should cache the non existence of a manifest in the registry cache, and not add anything to the settings file (this is what the old extension used to do).

[kitsonk]

Yeah, that makes sense... will work on a fix.