Simplify the ability to write typemaps

[Dushistov]

The new syntax should be similar to code below.

This should help to resolve several issues:

1. add Rust(std::option::Option) <-> Java(X) mapping #11 at now it is impossible to handle conversation of Option<T> and Option<&T> at once,
   because of Rust trait doesn't allow this, see rust Spurious "downstream crates may implement trait ..." rust-lang/rust#50238 and Spurious "note: downstream crates may implement trait Foo for type &_" rust-lang/rust#48869
2. Passing repr(C) struct by value #167 should simplify transfer of #[repr(C)] between C++<->Rust
3. Support Option as value of Result? #133 It would be possible in user's Rust code write how to handle Result<Option<

foreign_typemap!(
    define_c_type!(
	#[repr(C)]
	struct concat_ident!(CFnOnce, swig_c_type!(T)) {
	    cb: extern "C" fn(swig_c_type!(T), *mut c_void),
	    ctx: *mut c_void,
	})
        
    (rust, <T, F: FnOnce(T)> $r_param: F) <= concat_ident!(CFnOnce, swig_c_type!(T))
    {
	  |x| $c_param.cb(convert_to_c!(x), $c_param.ctx)
    }

     define_helper_f_helper!(
	 void concat_ident!(result_ready, swig_c_type!(T))(swig_c_type!(T) ret, void *ctx)
	 {
	     swig_f_type!(T) cpp_ret = convert_to_f!(ret);
	     auto ptr = std::make_shared<swig_f_type!(T)>(std::move(cpp_ret));
	     auto fi =
		 static_cast<QFutureInterface<std::shared_ptr<swig_f_type!(T)>> *>(ctx);
	     fi->reportResult(std::move(ptr));
	     fi->reportFinished();
             delete fi;
	 }
     )
    (f, input_to_output) => r#"QFuture<std::shared_ptr<swig_f_type!(T)>>"# r#"
        auto fi = new QFutureInterface<std::shared_ptr<swig_f_type!(T)>>;
       concat_ident!(CFnOnce, swig_c_type!(T)) cb;
       cb.cb = concat_ident!(result_ready, swig_c_type!(T));
       cb.ctx = fi;
       $f_result = fi->future();
       $c_result = cb;
 }"#
);


foreign_typemap!(
    (rust, &str) => RustStrView {
        RustStrView::from_str($r_param)
    }
    (f) => QString r#"
$f_result = QString::fromUtf8($c_result.data, $c_result.len);
"#);

Missed features:

1. Temporary variables in rules
2. Combining generic rules with $out
3. Optimization

[Dushistov]

Combining generic rules with $out

This is only missed. it will be addressed if someone need it.