Get emmet completions from css extension

[ramya-rao-a]

• Use the "next" version of LS protocol,server and client to get the new completion trigger kind
• Use emmet helper to get emmet completions at the right places in html,css,less,scss files
• Re-parse the document and get the non-emmet completions only for new completion requests
• For completion requests that's meant to complete a previous incomplete request, use the cached non-emmet completions from previous request + new emmet completions
• Basic Tests