Signature documentation consumes entire frame

[WhiteExponent]

Describe the bug

When lsp-signature-render-documentation is non-nil, with some functions, the displayed documentation is so large that it occupies almost the entire frame.

To Reproduce
Note: This could probably be encountered in any language, but here I am giving the example that I encountered.

1. Install python-language-server
2. Find a Python buffer
3. Enter open(, and a very large documentation section should open up in the echo area.

Expected behavior
The documentation should (IMO) be limited to at most half the frame, as if it was split with C-x 2.

Which Language Server did you use
lsp-python, but I think it will happen with any language server that supports documentation.

OS
Debian GNU/Linux 10

Screenshot

[yyoncho]

I propose showing N lines from the docs by default and having a shortcut to toggle from the full docs to the N lines docs.

[yyoncho]

Alternatively we may simply limit the size of the LV window.

[yyoncho]

• added lsp-signature-doc-lines (default 20) to limit the number of lines to show from the docs
• added function to toggle from full/truncated view - lsp-signature-toggle-full-docs (bound to M-a by default in the signature map).