Provide diagnostic option to enable on-demand schema loading

[nesterone]

VSCode supports on-demand loading of url content for $schema, it's a part of
Microsoft/vscode-json-languageservice, however, it's not available through monaco-editor

Such functionality would be a good plus, for example it was requested in vega/editor/issues/33 and I see similar feature request here microsoft/monaco-editor/issues/365

[msftclas]

All CLA requirements met.

[nesterone]

Hi, @aeschli
Any comments on this?
I'm open to providing any correction to push that feature ;-)

[aeschli]

Oh, I see, fetch now works in web workers on Chrome. It would be cool to also have this working in other browsers.
Other than that the PR looks fine, I added some remarks.

[nesterone]

Hi, @aeschli
Can't find any remarks from you

[aeschli]

Actually, the code will always check the schemas provided through the schemas property first, and if nothing found, will use the requestService

[nesterone]

Hi, @aeschli
I've removed part about existing functionality

[nesterone]

Hi, All
Any plans to merge PR ?

[rebornix]

Gentle ping for @aeschli

[aeschli]

@nesterone Can you remove the version change from package.json? We will do that when releasing the next editor version.

[aeschli]

Thanks @kuzya-zz !

[themez]

I've met a problem that the schema resource needs credentials, can I set a custom schemaRequestService?

schemaRequestService = function (url) { 
  return fetch(url,{
    credentials: 'include'
  }).then(response => response.text())};