Simplify the tree-sitter parser creation API

["Daniel Martín" <mardani29@yahoo.es>]

Currently, there are three functions to create a tree-sitter parser:

- treesit-get-parser-create
- treesit-get-parser
- treesit-parser-create

I think this set of similarly named functions can be reduced, so that
developers don't need to remember a lot of APIs.  How I understand the
problem of creating a tree-sitter parser is that we need three things
from the developer:

- A programming language (a symbol).
- A buffer (optional, default to the current buffer).
- Whether to create or reuse an existing parser for that language.

I think it would be simpler to have just one parser creation API like

(treesit-make-parser LANGUAGE &optional BUFFER ALWAYS-NEW)

There are similar API patterns like this one already in Emacs.  With
this proposed API, the common case, which is to create a parser for the
current buffer, and to try to reuse one if it already exists, is very
simple from the POV of an ELisp developer integrating with tree-sitter:

(treesit-make-parser 'c)

Any thoughts?