Languageclient-neovim: Support multi-line textDocument/hover

[MaskRay]

Currently textDocument/hover is implemented via

    @neovim.function("LanguageClient_textDocument_hover")
    @deco_args
    def textDocument_hover(self, uri: str, languageId: str,
........
        echo(info)

# state.py
def echo(message: str) -> None:
    """Echo message."""
    message = escape(message)
    execute_command("echo '{}'".format(message))

For multi-line macro/struct/class declaration and comment support (see jacobdufault/cquery#29 for cquery's ongoing support), this UI may be infeasible. We might need to provide an alternative UI (e.g. preview window)

[YaLTeR]

Maybe it's possible to display the info in a "popup" similar to autocomplete suggestions?

EDIT: this is kinda related to https://github.com/autozimu/LanguageClient-neovim/issues/196

[stellarhoof]

Also, don't use echomsg if possible. It pollutes the messages history.

[prabirshrestha]

vim-lsp supports multiline hover. Feel free to port this related commits.

• https://github.com/prabirshrestha/vim-lsp/commit/203d682e30ca30d995fdceaf53df8a7808409baa
• https://github.com/prabirshrestha/vim-lsp/commit/d3af2b8e1a6d15edab49410e1c1f60deef1d654c