This commit is a prototype exploring what it would mean to make the
minor mode work with the built in `treesit.el` treesitter support in
Emacs 29. I've modified many of the functions and fold rules specific
to the ruby language, and have tested locally with a few ruby code
files to confirm things are working

The actual work consists mostly of ...
* swapping out functions for their `treesit.el` equivalents
* replacing symbols for node types with strings
* Modifying `(alist-get...` usages to support string keys

Not sure why this is needed but I get startup errors without these.
Perhaps an ordering issue.

`(car fold-range)` is not a sequence, it's a symbol, at least in my
C++ buffers. This patch converts it using `symbol-name`.

For simplicity I just converted the `patterns` vector to a list, but
there are probably simpler ways to do this.

It seems `treesit-buffer-root-node` returns an error when there is no
parser for a given buffer. In my case, this happens when trying to get
doc for an elisp variable; `ts-fold--tree-sitter-trigger` runs in an
elisp-mode "*temp*" buffer, and `treesit-buffer-root-node` raises an
error.
If I just ignore the error around that call,
`ts-fold--tree-sitter-trigger` still runs `(ts-fold-mode -1)`. Seems
like the simplest thing is to just do nothing in that case.

To repro the problem, enable ts-fold mode globally and do `C-H v
emacs-version`.

This is not perfect; when folding a node with children, it shows the
first character of the node, then the fold indicator, then the colon.
Ideally it would show the whole name of the key, and then the fold
indicator. Not sure how to do that.

- Use a better ts-fold-range function for yaml
- Remove "block_sequence" fold-parser; don't think that's useful.
- Fix ts-fold--get-nth-child: `(treesit-node-children) is a list, not
  an array.

treesit.el patches

Some c-preproc-if have no 'else' branch and 'alternative' node.
For example:

CODE:
  #if THREAD_SIZE >= PAGE_SIZE
  void __init __weak thread_stack_cache_init(void)
  {
  }
  #endif

TREE:
(preproc_if #if
 condition: (binary_expression left: (identifier) operator: >= right: (identifier))
 \n
 (declaration type: (primitive_type) declarator: (identifier) type: ;)
 (function_definition type: (type_identifier)
  declarator:
   (function_declarator declarator: (identifier)
    parameters:
     (parameter_list (
      (parameter_declaration type: (primitive_type))
      )))
  body: (compound_statement { }))
 #endif)

So we use last child node(i.e. "#endif") instead of 'alternative' node in this case.

Fix folding of c-preproc-if