ast, parser, fmt: fix fmt error of infix expr with comments (fix #17560)

[yuyi98]

This PR fix fmt error of infix expr with comments (fix #17560).

• Fix fmt error of infix expr with comments.
• Add test.

infix_expr_with_comments_keep.vv

fn main() {
	a := 4 // comment1
	 + /* comment2 */ 6

	b := 5 /* comment1 */ + // comment2
	 6

	c := 4 /* comment1 */ + /* comment2 */ 6 // comment3
}

[medvednikov]

Inline comments are tricky with our implementation. I think it's better to ban them.

Otherwise we'd have to re-write comments entirely, handle them like in Go.

Although this PR seems to handle a large percentage of them.

[yuyi98]

Inline comments are tricky with our implementation. I think it's better to ban them.

Very much agree with this just like zig.