ZJIT: Add codegen for Insn::FixnumDiv

[k0kubun]

Leaving a small issue for newcomers.

We don't support compiling Integer#/ calls yet. gen_insn of zjit/src/codegen.rs should handle Insn::FixnumDiv and do something similar to jit_rb_int_div in yjit/src/codegen.rs.

[dddictionary]

@aidenfoxivey and I are planning on taking a look at this!