Add Prolog tree-sitter grammar

[mkorje]

This PR adds a tree-sitter grammar for Prolog. It uses https://codeberg.org/foxy/tree-sitter-prolog, a fork/rewrite of https://github.com/Rukiza/tree-sitter-prolog.

I've probably made a mistake in how the runtime/queries/prolog/* files should be done, sorry about that! The changes in this PR seem to be working for me, though I'd appreciate it if others could try it out and ensure it works for them.

[the-mikedavis]

The captures need some tweaks to match the scopes we use: https://docs.helix-editor.com/master/themes.html#syntax-highlighting

For example boolean should be constant.builtin.boolean, number should be constant.numeric.integer or constant.numeric.float

[the-mikedavis]

These are written for neovim's indentation system. Ours has different captures: https://docs.helix-editor.com/master/guides/indent.html

We could remove this file to use the default indentation and indents queries could be contributed as a follow-up

[gruhn]

I think there is a problem with multi-line comments, but that's probably a problem with the grammar, right? For example, the following code is highlighted like one big comment:

/* first comment */

plus(X, Y, Z) :- 
	Z is X + Y.

/* second comment */

Although, if I remove the second comment, then the predicate plus is not highlighted like a comment.