Issues with documentation popup for LSP code completion

[kaloyan-raev]

The documentation popup for LSP code completion has some shortcomings:

• No scrollbars
• The documentation is displayed in plain text. Although LSP does not enforce any particular format yet (see Proposal: treat CompletionItem#description as markdown microsoft/language-server-protocol#111), popular documentation formats like JavaDoc and PHPDoc contain HTML tags. It would be better to render them instead of displaying them raw, thus making the documentation more readable.
• Clicking on the popup hides it, thus making impossible to select and copy some text from the documentation.
• Flickering of the popup while typing

Reproduction Steps:

1. Build from the latest master.
2. Start a workspace with the PHP stack and some project sample.
3. Open the PHP editor.
4. Invoke code completion and wait for the documentation popup to appear.

Expected behavior:

• Scrollbars when necessary
• HTML tags are rendered
• Possible to select and copy some text from the documentation
• No flickering while typing

Observed behavior:

Che version: latest master
OS and version: Fedora 24
Docker version: 1.10.3
Che install: server (zip)

Additional information:

• Problem started happening recently, didn't happen in an older version of Che: [No]
• Problem can be reliably reproduced, doesn't happen randomly: [Yes]