Consolidate treesit parser create functions

Consolidate treesit parser create functions

Merge treesit-parser-create, treesit-get-parser,
treesit-get-parser-create into one: treesit-parser-create.

* src/treesit.c (Ftreesit_parser_language): make BUFFER parameter
optional, add new parameter NO-REUSE.  Optionally reuse parser.
* test/src/treesit-tests.el: Change all parser creation to use
treesit-parser-create.  Remove tests for the removed functions.
* lisp/treesit.el (treesit-get-parser, treesit-get-parser-create):
Remove.
* lisp/treesit.el (treesit-set-ranges, treesit-get-ranges)
(treesit-buffer-root-node, treesit-query-string)
(treesit-font-lock-fontify-region, treesit-search-forward)
(treesit-query-validate): Change to use treesit-parser-create.