support for outshine mode

[jave]

I like using outshine mode in clojure-mode buffers, but folding doesnt appear to work in clojure-ts mode.

https://github.com/alphapapa/outshine

[bbatsov]

Seems that's some extension of the built-in outline-mode. Probably we haven't implemented properly the support for outline, as I doubt outshine requires something special. Should be an easy task.

[rrudakov]

FYI, we need to define proper value for treesit-outline-predicate. From the documentation:

treesit-outline-predicate is a variable defined in ‘treesit.el’.

Its value is ‘treesit-outline-predicate--from-imenu’

Predicate used to find outline headings in the syntax tree.
The predicate can be a function, a regexp matching node type,
and more; see docstring of ‘treesit-thing-settings’.
It matches the nodes located on lines with outline headings.
Intended to be set by a major mode.  When nil, the predicate
is constructed from the value of ‘treesit-simple-imenu-settings’
when a major mode sets it.

[bbatsov]

Yeah, that's what I figured as well.