Fix treesit-parser-create behavior regarding indirect buffers

Fix treesit-parser-create behavior regarding indirect buffers

The previous fix fixed the problem that treesit-parser-create
always use the current buffer, but that introduce another subtle
problem: if an indirect buffer creates a parser, the parser
saves the base buffer rather than the indirect buffer.  In Emacs
29, if you create a parser in an indirect buffer, the parser
saves the indirect buffer.  This change of behavior breaks some
existing use-cases for people using indirect buffer with
tree-sitter.

In Emacs 31, indirect buffers and base buffer get their own
parser list, so this problem doesn't exist anymore.  The fix is
only for Emacs 30.

* src/treesit.c (Ftreesit_parser_create): Use the buffer that's
given to treesit-parser-create, even if it's an indirect buffer.